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COLLEGE  OF 

PHYSICIANS  AND  SURGEONS 

LIBRARY 

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, 

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Gift   of 

Dr.   0.   S.   Strong 

Digitized  by  tlie  Internet  Arcliive 

in  2010  with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/physiologypractiOOwild 


"I  have  been  in  the  hnbit  of  advisiug  my  students  to  dissect  the  CAT  as  a  convenient  prelitpiaavv  [to 
practical  Human  Auatoniy."— yo^d*^/!  Leidy. 

"It  seems  to  me  that  the  first  dissections  should  be  made  on  CATS  and  doj^s  until  a  good  technique  has 
been  acquired,  so  that  the  supply  of  human  cadavers,  which  is  always  insufficient,  can  be  fully  utilized  to 
the  best  advantage."— y.  6".  Billings. 

"There  is  so  close  a  solidarity  between  ourselves  and  the  animal  world  that  our  inaccessible  inward 
parts  may  be  supplemented  by  theirs.  A  SHEEP'S  heart  or  lungs  or  eve  must  not  be  confounded  with 
those  of  man  ;  but  so  far  as  the  comprehension  of  the  elementary  facts  of  the  physiology  of  circulation  and 
of  respiration  and  of  vision  goes,  the  one  furnishes  the  needed  anatomical  data  as  well  as  the  other." — 
Huxley. 


Physiology  Practicums 

KXPI.ICIT   DTRECTIONS    FOR    EXAMINING 

PORTIONS    OF    THE  CAT,  AND   THE    HEART,  EYE, 
AND   BRAIN   OF  THE   SHEEP 

AS    AN    AID    IN    THE 

STUDY    OF    ELEMENTARY  PHYSIOLOGY 

SECOND  EDITION,   REVISED 
WITH    THIRTY    KIGTJRKS 


BURT   G.  WILDER,  B.S.,  M.D., 

Professor  of  Physiology,  Vertebrate  Zoology,  and  Neurology  in  Cornell  University  ;  formerly 
Professor  of  Physiology  in  the  Medical  School  of  Maine  and  the  University  of 
Michigan  ;   President  ( 1 885)  of  the  American  Neurological  Asso- 
ciation and  of  the  Biological  Section  of  the  Amer. 
Association  Adv.  Science,  etc. 


PUBLISHED    BV    THE    AUTHOR 

PRE.SSES    OK   THE    ITHACA   JOURNAL 

I«95 


COPYRIGHT,    1893,    1895,    BY   BURT   G.  WILDER.      ALL   RIGHTS    RESERVED. 

Price,  |i.oo,  post-paid.     Address  the  author,  Ithaca,  N.  Y. 
/ji  Preparation  :     How  to  Prepare  Specimens  for  Physiology  Practicums. 


By  the  author :  Dissection  of  the  Sheep's  Brain  :  being  part  IV  of  Physiology  Practicums, 

with  Plates  XVIII-XXV  and  an  Appendix  on  the  Removal    and 

Preservation  of  the  Brain.    Price  40  cts.,  post-paid. 


By  the  author  and  S.  H.  Gage  :  Anatomical  Technology  as  Applied  to  the  Domestic  Cat  : 

an  Introduction  to  Human,  Veterinary,  and  Comparative  Anatomy.     Third, 

from  the  second  revised,  edition.     Pp.  600,  120  figs,  4  lithograph 

plates.     A.  S   Barnes  &  Co.,  New  York,  1892.     I4.50. 


By  Simon  Henry  Gage,  Professor   of  Anatomy,  Histology   and  Embryology   in   Cornell 

University  :  The  Microscope  and  Microscopical  Methods.    Fifth  edition,  rewritten, 

greatly  enlarged,  and  illustrated  by   103  figures  in  the  text.     Price  |i. 50 

post-paid.     Comstock  Publishing  Co.,  Ithaca,  N.  Y.,  U.  S.  A. 


PREFACE  TO   THE   FIRST   EDITION. 


About  ten  years  ago,  in  the  effort  to  enable  the  members  of  the  gen- 
eral class  in  Plnsiology  at  Cornell  University  (150-180  in  number)  to 
study  for  themselves  intelligently  certain  parts  of  the  cat  and  sheep  as  an 
aid  to  the  comprehension  of  the  functions  and  relations  of  the  correspond- 
ing human  organs,  I  put  alcoholic  specimens  before  them  and  wrote  on 
the  blackboard  brief  directions  which  were  orally  amplified  and  illustra- 
ted. A  few  years  later  these  directions  were  written  upon  cloth  sheets 
that  were  suspended  before  the  class.  They  were  amplified  and  printed 
in  the  fall  of  1S89  and  issued  in  their  present  form  in  1892. 

The  separation  of  the  sheets  and  plates  has  obvious  inconveniences 
but  upon  the  whole  the  practical  advantages  are  greater. 

From  the  first  the  assistants  and  students  have  cordially  cooperated 
toward  increasing  accurac)'  and  explicitness. 

It  is  to  be  hoped  that  ere  long  as  much  as  is  here  included  may  be 
required  for  admission  to  this  and  other  universities,  so  that  the  instruc- 
tion therein  may  commence  upon  a  foundation  both  higher  and  more 
substantial  than  at  present. 

Ithaca^  N.    F. ,  December  26,  i8gj. 

PREFACE  TO   THE   SECOND   EDITION. 


The  text  has  been  revised  and  largely  rewritten.  An  effort  has  been 
made  to  correct  the  errors  and  omissions  detected  during  the  three  years' 
use  of  the  work  at  Cornell  University  and  elsewhere.  For  helpful  sug- 
gestions I  am  particularlv  indebted  to  my  assistants,  Dr.  P.  A.  Fish  and 
Dr.  B.  B.  Stroud. 

The  changes  in  the  illustrations  comprise  new  figures  of  the  cat's 
skeleton,  and  of  the  sheep's  heart  and  brain.  Two  outlines  have  been  in- 
troduced into  the  text. 

The  order  has  been  modified  so  as  to  bring  the  examination  of  the 
head  and  neck  just  before  that  of  the  eye  and  brain.  The  eleven  practi- 
cums  are  combined  so  as  to  form  four  Parts,  each  dealing  with  a  natural 
group  of  subjects. 

A  teaching  experience  of  twenty-seven  years  leads  me  to  believe  that 
explicitness  should  be  a  main  feature  of  directions  for  beginners.  To 
credit  them  with  unlikely  knowledge,  jtidgment  and  skill,  or  with  inspir- 
ation that  will  serve  in  place  of  those  attributes,  may  compliment  them 
and  simplify  the  task  of  the  writer.  But  there  result  perplexities,  the 
formation  of  faulty  methods,  and  the  waste  of  time  and  material. 

When,  however,  there  has  once  been  established  a  sound  basis  of 
fact  and  manipulation,  the  student  may  safely  and  profitably  venture  upon 
unfamiliar  ground.  He  may  either  apply  the  directions  to  different 
forms,  or  re-examine  the  same  forms  in  different  ways.  For  example,  the 
brain  of  the  cat,  dog,  monkey  or  man  may  compared  with  that  of  the 
sheep,  and  the  sheep's  brain  may  be  explored  in  ways  other  than  that 
presented  in  the  following  pages. 

September  20,  i8g^. 


CONTENTS. 


PRACTICUM.                                      SUBJECT.  PAGES.              PLATES'. . 

fH  t     The  Cat  :  Its  Form,  Skeleton,  Skin-Muscles,  and  Axillary 

^  >-<         /         Vessels  and  Nerves 5-8                    I-IV 

Ph          I^.     Dissection  of  the  Cat's  Arm 9-16       I,  II,  IV,  V, 

I 

fH         Iljl.     Thoracic  Viscera  of  the  Cat 17-23             VI-VIII 

^S      liV.     The  Abdomen  of  the  Cat 23-28            VIII-XI 

Oh            W.     The  Heart  of  the  Sheep 29-36           XII-XIV 

Si-;      ■^I.     The  Head  and  Neck  of  the  Cat 37-48         XV-XVII 

<t:    Vfl.     The  Eye  of  the  Sheep 47-52         XVII-XX 

VIII.     The  Brain  of  the  Sheep  :  its  Ectal  Features  and  Segmen- 
tal Constitution  49-53    XVIII-XXII 

fi    _     IX.     The  Mesal  Aspect  of  the  Sheep's  Brain  ;  Endymal  Con- 

^  >                  tinuity  and  Ccelian  Circumscription 54-62    XXIII-XXV 

P^'~'       X.     Dissection  of  the  Sheep's  Brain . 6367 

XI.     Dissection  of  the  Brain  continued  ;  Study  of  its  Transec- 
tions   68-74    XVIII-XXV 


LIST  OF  PLATES. 


Plate  I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

Vljl. 

IX. 

X. 

xt;: 

XIII. 
XIlV. 

XV. 
X'tl. 

xyiii. 

XVIII. 
XIX. 
XX. 


XXIII. 
XXIV. 
XXV. 


The  Skeleton  of  the  Cat.     From  Straus-Durckheim's  "Anatomic  du  Chat." 

The  Ectal  Muscles  of  the  Cat,  seen  from  the  Left  Side. 

Ventral  Aspect  of  the  Cat's  Thorax. 

Right  Axillary  Region  of  the  Cat  after  division  of  the  Pectoral  Muscles. 

Right  Arm  of  Cat,  partly  dissected. 

Thorax  of  the  Cat,  opened  from  the  Right  Side  to  show  the  Lungs. 

The  Cat's  Thorax,  after  removal  of  the  Right  Lung. 

Diaphragm  of  the  Cat,  its  Cephalic  or  Thoracic  Aspect. 

Abdominal  Viscera  of  the  Cat,  from  the  Left  Side. 

Abdominal  Viscera  of  the  Cat,  after  removal  of  the  Small  Intestine. 

Pelvic  Viscera  of  the  Female  Cat. 

Ventral  and  Dorsal  Aspects  of  the  Sheep's  Heart.     Two  figures. 

Heart  of  the  Sheep,  the  Right  Auricle  opened. 

Heart  of  the  Sheep,  the  Left  Side  opened. 

The  Salivary  Glands  of  the  Cat.     From  "Anatomical  Technology." 

Head  and  Neck  of  the  Cat,  from  tlie  Left  Side,  partly  dissected. 

Mesal  Aspect  of  the  Right  Half  of  the  Cat's  Head.  From  "Anatomical  Technol- 
ogy" and  "Reference  Handbook  of  the  Medical  Sciences." 

Braiu  of  the  Sheep,  the  Cerebrum  sliced  to  near  the  level  of  the  Callosum. 

Ventral  Aspect  of  the  Sheep's  Brain,  the  Eyes  attached. 

Ventral  Aspect  of  the  Sheep's  Brain  after  the  removal  of  the  Hypophysis  and 
Parts  of  the  Cerebrum  and  Cerebellum. 

Left  Side  of  the  Sheep's  Brain  after  removal  of  most  of  the  Cerebrum  and  Cere- 
bellum. 

Dorsal  Aspect  of  the  Sheep's  Brain  after  removal  of  parts  of  the  Cerebrum  and 
Cerebellum. 

Mesal  Aspect  of  the  Right  Half  of  the  Sheep's  Brain. 

Sheep's  Brain,  the  Paracoeles  (Lateral  Ventricles)  exposed. 

Transection  of  the  Sheep's  Brain  at  the  level  of  the  Medicommissure  ;  Part  of 
the  same  enlarged.     Two  figures. 


FIGURES  IN  THE  TEXT. 


Fig.  I,  p.     6,   Left  Side  of  the  Cat. 

Fig.  2,  p.   19.  Right  Side  of  the  Cat's  Thorax,  showing  Lines  of  Incision. 

figure  is  wrongly  numbered  6. 
Fig.  3,  p.  69.  Dissection  of  the  Left  Olfactory  Bulb  of  the  Sheep. 


On  p.  ig  this 


PHYSIOLOGY  PRACTICUMS. 


PART      IV.       THE    BRAIN. 


PRACnCUM  VIII.     THE  GENERAL   FEATURES  AND  SEGMENTAL 
CONSTITUTION  OF  THE  BRAIN. 

PI,ATES    REOUIRED  :    XVIII-XXIII. 


Suggestion . — The  comparative  unt'ainiliarity  of  most  students  with  the  parts  of  the 
brain  and  with  their  names  renders  it  particularly  desirable  that  the  directions  should  be 
read  and  the  plates  examined  in  advance  of  the  practictirn. 

Caution. — The  specimens  should  not  be  allowed  to  dry.  Dip  them  occasionally  in 
alcohol  or  formalin,  or  hold  them  over  a  dish  of  it  and  squeeze  some  upon  them  from  a 
pledget  of  absorbent  cotton. 

§  I.  General  Topography  of  the  Sheep' s  Brain. — Determine  the 
regions  and  aspects  as  follows  : 

a.  As  a  whole  the  brain  is  obviously  symmetric,  i.  e.^  composed  of 
right  and  left  halves  approximately  identical,  notwithstanding  artificial 
differences  due  to  injury  during  removal  from  the  skull  or  to  distortion 
during  hardening. 

b.  The  two  ends  differ,  in  that  one  presents  a  single,  mesal  or  azy- 
gous  projection,  the  remnant  uf  the  myel  (spinal  cord),  while  at  the  other 
there  is  a  mesal  notch  between  the  two  OLFACTORY  BULBS  ;  the  latter,  of 
course,  is  the  cephalic  end,  and  the  former  the  caudal. 

c.  Of  the  two  remaining  aspects,  the  more  regularly  convex  is  dorsal.^ 
while  the  ventral  \s  irregular  and  presents  several  elevations  and  depres- 
sions. 

§  2.  Close  the  eyes,  handle  the  brain,  hold  it  in  various  positions, 
and  test  the  prompt  recognition  of  the  several  regions  by  the  touch. 

§  3.  Great  Divisions. — By  a  transverse  depression  the  caudal  fourth  is 
demarcated  from  the  cephalic  three-fourths.  The  former  consists  mostly 
of  the  CEREBELLUM,  the  latter  mostly  of  the  cerebrum  Note  that  the 
cerebrum  presents  a  mesal  furrow^  while  the  cerebellum  is  highest  at  the 
meson  ;  also  that  the  cerebral  surface  is  cut  up  into  tracts,  g^•res  or  GYRI, 
by  sinuous  furrows,  fissures,  while  the  cerebellum  presents  several  series 
of  jiarallel  narrow  ridges,  FOLIUMS,  and  alternate  short  furrows,  rimulas. 
a.  The  human  cerebellum  presents  a  furrow  between  two  lateral  masses,  but  with 
most  mammals  the  form  is  more  nearly  as  in  the  sheep. 

§4.  Make  an  outline  drawing  of  the  left  side  of  the  entire  brain, 
natural  size,  indicating  the  following  features  : 

a.  The  irregular  ventral  outline,  which  at  present  serves  merely  as 
a  base-line  for  the  rest  and  need  not  be  accurately  represented. 

b.  The  convex  dorsal  outline,-  with  its  abrupt  cephalic  and  caudal 
declivities,  and  the  oblique  furrow  between  the  cerebrum  and  the  cere- 
bellum. 


go  Practieum    VIII.     The   Sheep's   Brain.  .  ^ 

c.  The  caudal  projection  of  the  myeh 

d.  The  slight,  cephalic  e,\teiisioii  of  the  left  olfactor}'  bulb. 

e.  The  numerous  subdivisions  of  the  cerebrum  and  cerebelhim  -need 
not  be  indicated,  but  the  following  should  be  : 

f.  The  line  separating  the  foliated  cerebellum  proper  from  the 
OBLONGATA  constitu'ing  the  ventral  portion  of  that  region.  '. 

g.  Two  or  three  lines  approximately  parallel  with  the  main  outline 
of  the  cerebellum,  demarcating  the  mesal  and  one  or  two  lateral  series  of 
foliums. 

h.  On  the  cerebral  region,  a  line  beginning  at  the  root  of  the  olfac- 
tory bulb  and  extending  dorso-caudad  to  the  middle  of  the  length  of  the 
cerebrum,  then  caudad  and  slightly  ventrad.  The  convoluted  mass  dor- 
sad of  this  line  is  the  cerebrum  proper,  pallium  or  mantle  ;  the  ventral 
portion,  although  sometimes  corrugated  in  parts,  is  not  stricth'  convol- 
uted, and — from  its  direct    continuity  with  the  olfactory   bulb — is  called 

the  OLFACTORY  TRACT. 

§5.  Make  an  outline,  uatural  size,  of  the  base  or  ventral  aspect  of 
the  brain.  PL  XIX  may  be  employed  for  comparison,  and  for  ascertain- 
ing the  names  of  parts,  but  the  drawing  should  represent  the  specimen. 
The  following  order  will  be  found  most  available  : 

a.  Represent  the  meson  by  a  straight  line  the  length  of  the  brain, 
but  light  enough  to  permit  portions  to  be  erased  later;  then  the  lateral 
outlines  of  the  whole  and  tlie  boundary  between  the  cerebral  and  cere- 
bellar regions. 

b.  All  the  parts  and  lines  already  noted  from  the  lateral  aspect,  the 
olfactory  bulbs  and  tracts  and  their  lateral  bonndaries  ;  the  lines  between 
the  cerebelhnn  and  the  oblongata. 

c.  Tlie  PONS,  a  bridge-like  mass  whose  elevated  cephalic  margin 
corresponds  with  the  boundary  between  the  cerebral  and  cerebellar 
regions  and  which,  laterad,  is  evidently  continuous  with  the  cerebellum. 

d.  The  mesal  furrow  upon  the  cephalic  part  of  the  cerebrum  is  in- 
terrupted abruptly  by  an  x-shaped  elevation,  the  chiasma.  On  PI.  XIX 
is  seen  that  the  cephalic  diverging  arms  of  the  x  are  continued  laterad  to 
the  eyeballs  ;  they  are  the  optic  nerves.  The  caudal  arms,  less  distinct 
in  the  actual  specimen,  are  the  OPTic  tracts. 

e.  Between  the  chiasma  and  the  pons  should  be  a  mesal,  sub-splier- 
ical  mass,  the  HYPOPHYSIS,  as  shown  in  PI.  XIX,  connected  with  the 
base  of  the  brain  proper  at  three  or  four  points  ;  the  most  important  of 
these  attachments  is  at  the  middle  of  the  cephalic  border. 

In  the  actual  brain  any  one  of  the  following  conditions  may  exist  : 
I.  The  hypophysis  may  be  cut,  torn  by  the  saw,  or  flattened  by 
pressure.  2.  The  mesal  pedicle  above  mentioned  may  present  an  artifi- 
cial orifice  through  which  preservative  was  injected  into  the  cavities  of 
the  brain.  3.  The  entire  hvpophysis  may  be  cut  or  torn  off,  leaving  a 
mesal  orifice,  the  lura,  as  in   PI.  XX. 

/  In  the  interval  at  either  side  of  the  hypophysis  is  the  CRUS,  a 
column-like  mass,  overlapped  laterad  by  the  margin  of  the  olfactory 
tract,  and  caudad  emerging  from  entad  of  the  pons. 

§  6.  The  Arachnoid. — The  outlines  of  the  parts  just  mentioned  are 
somewhat  vague.  If  the  brain  be  supported  on  the  fingers  of  both  hands, 
and  the  thumbs  be  placed  on  the  widest  and  most  prominent  part  of  the 
olfactorv  tracts  (corresponding,  on  PI.  XIX,  to  the  letters  /  0  rji/ on  one 
side  and  on  the  other  to  the  area  laterad  of  the  numbers  4  and  (5),  and  the 
parts  be  pressed  alternately  laterad  and  me.sad,  there  will  be  recognized  a 


Practieum   VIII.     The    Pia,  Vessels,  and  Nerves.  SI 

slieet  of  membrane  which  is  alternately  tense  and  wrinkled.      This  mem- 
brane is  the  ARACHNOID. 

§7.  The  Subarachnoid  Space. — At  the  (real)  left  of  the  hypophysis, 
with  the  forceps  tear  the  arachnoid  ;  there  will  be  disclosed  an  interval 
between  it  and  the  apparent  surface  of  the  brain  ;  the  subarachnoid 
SPACE.  Note  similar  conditions  in  the  following  localities  :  {a)  In  the 
triangnlar  interval  between  the  crns,  the  pons,  cerebellum,  and  cerebrum  ; 
{b)  in  the  deeper  interval  between  the  cerebrum  and  cerebellum  when 
the  latter  is  tilted  caudad  ;  (r)  between  the  two  halves  of  the  cerebrum  ; 
[d)  between  the  dorsum  of  the  m\el  and  the  overhanging  cerebellum  ;  {e) 
between  the  margins  of  the  olfactory  bulbs  and  the  adjacent  cerebral  sur- 
face ;  (/)  along  the  lines  of  the  principal  fissures  and  rimulas. 

Upon  the  intervening  areas  the  arachnoid  may  be  recognized  as  con- 
stituting the  surface,  but  as  adhering  closeh'  to  what  is  subjacent. 

g8.  The  Pia. — After  the  removal  of  the  arachnoid  from  tlie  crus  at 
the  left  of  the  hypophysis  there  will  be  disclosed  BLOOD-VESSELS  and  a 
fibrous,  delicate  sheet  of  tissue,  the  pia,  which  adheres  quite  closely  to 
the  brain  substance.  To  facilitate  this  examination  the  hypophysis  may 
now  be  pulled  off.  The  pia  will  be  seen  to  follow  closely  all  the  contours, 
and  to  dip  to  the  bottom  of  the  mesal  cleft  caudad  of  the  elevation, 
TUBER,  wiiich  supported  the  hypophysis. 

a.  In  the  first  edition  this  was  called  torus.  Tuber  is  to  be  preferred 
as  a  simple  reduction  of  the  name  commonly  emploved,  tuber  cinereum. 

§9.  The  Blood-vessels  of  the  Pia. — The  decided  resistance  to  the 
removal  of  the  pia  at  this  point  is  due  to  the  considerable  number  of  ves- 
sels which  leave  it  and  enter  the  substance  of  the  brain.  With  a  lens  mav 
be  recognized  the  holes  (vascular  foramina)  transmitting  these  vessels, 
whence  the  names  given  to  the  triangular  area,  posTCRIBRUm  and  "pos- 
terior perforated  space."  With  less  ease,  all  surfaces  denuded  of  the 
pia  may  be  seen  to  be  finely  punctate,  as  if  by  pin  pricks,  and  the  ental 
surface  of  the  pia  to  present  a  woolly  aspect  called  tomentum,  from  the 
large  number  of  broken  vessels  ;  see  Handbook,  VIII,  Fig.  4687,  and  §  11. 

§  10.  The  Cranial  Nerves. — Upon  the  lateral  part  of  the  pons  is  a 
fibrotis  cord  resembling  the  optic  nerve  ;  it  is  the  rojot  of  the  trigemin- 
us (trifacial  or  fifth),  the  sensitive  nerve  of  the  teeth  and  skin  of  the 
face,  etc.  If  pushed  from  side  to  side  it  will  be  seen  to  really  emerge 
from  the  brain  just  caudad  of  the  pons  or  perhaps  through  its  caudal  mar- 
gin ;  in  man  it  emerges  nearer  its  cephalic  margin. 

a.  The  other  cranial  nerves  are  smaller  and  apt  to  be  detached  with  the  pia,  but 
traces  of  them  may  be  seen  at  either  side  of  the  oblongata.  One,  the  oculo-motor,  springs 
from  the  crus  near  the  mesal  cleft  ;  on  PI.  XX  a  short  piece  of  it  is  shown  on  one  side  (the 
real  left,  apparent  right)  ;  on  the  other  the  slit  left  by  its  extraction  is  marked  j.  Another 
cranial  nerve,  the  troclilearis.  is  represented  on  PI.  XXII,  4. 

Note. — If  there  is  but  one  brain  available,  follow  the  directions  in  ^  11  upon  it  ;  if  two, 
upon  the  second  follow  the  directions  in  (!  12.  Adjoining  students  may  agree  which  they 
will  respectively  follow. 

§  II.  Alba  and  Cinerea. — With  the  large  scalpel,  dipped  in  alcohol, 
slice  off  the  dorsal  half  of  the  cerebellum,  avoiding  injury  to  the  cere- 
brum. The  cut  surface  will  present  two  colors,  the  ental  parts  lighter, 
the  ectal  darker.  The  former  is  the  alba,  composed  of  fibers  only  ;  the 
latter  the  ciNEREA,  consisting  of  fibers  and  cells.  If  the  alba  does  not 
extend  across  the  meson  renioxe  a  thin  slice  until  it  does.  Make  a  dia- 
grammatic drawing,  indicating  the  general  outline  and  the  tree-like 
branching  of  the  alba  toward  the  peripher\'. 


B2  Practicum  VIII.     The  Alba  and  Cinerea.  ' 

§  12.  Slice  oflf  the  caudal  third  of  the  cerebellum,  avoidino-  injury 
to  the  oblongata,  then  the  cephalic  third,  avoiding  injury  to  the  subjacent- 
parts. 

§13.  The  Cerebral  Alba  and  Cinerea. — Slice  off  the  dorsal  fourth. 
of  the  cerebrum.  Not  more  than  the  dorsal  fourth  should  be  removed  at 
the  first  section.  The  largest  available  scalpel  should  be  selected,  the 
blade  dipped  in  alcohol,  and  the  cut  made  with  a  slow  and  steady  sawhig 
movement.  The  plane  of  section  should  be  nearly  parallel  with  the  long 
axis  of  the  cerebrum  and  if  either  end  is  farther  ventrad  than  the  other 
let  it  be  the  cephalic. 

b.  .  On  either  cut  surface  note  the  relations  of  the  alba  and  cinerea  ; 
here,  as  also  in  the  cerebellum,  these  are  sometimes  called  more  specifi- 
eally  medulla  and  cortex.  The  cortex  forms  a  continuous  ectal  layer 
as  in  PL  XVIII,  following  the  fissures. 

a.  The  detached  areas  of  cinerea  represent  portions  of  the  cortex 
at  the  bottoms  of  fissures  that  open  on  the  dorsum. 

b.  At  the  ends  of  the  mesal  (intercerebral)  fissure,  note  the  arach- 
noid crossing  from  one  hemicrebrum  to  the  other  ;  near  the  caudal  end  is 
an  orifice  corresponding  to  i  in  PL  XXIII. 

c.  Divaricate  the  two  halves  of  the  removed  piece  and  note  that  the 
mesal  surfaces  are  covered  by  the  pia  which  also  dips  into  the  fissures. 

§  14.  Exposing  the  Callosiim. — On  Plates  XVIII  and  XXIII  note 
the  location  and  extent  of  the  callosum,  the  great  cerebral  commissure. 
Note  also  on  PL  XVIII  the  directions  of  the  several  oblique  surfaces  b 
and  c  which  are  approximately  at  45°  with  the  surface  a. 

§  15.  Apply  the  scalpel  across  the  middle  of  the  length  of  the  left 
olfactory  bulb  and  slice  oif  the  cephalic  end  of  it  and  of  the  left  cerebrum. 
If  the  piece  comes  off  freely  or  adheres  only  by  the  pia,  then  transect  the 
other  at  the  same  level  and  angle.  But  if  it  hangs  to  the  opposite  side  by 
any  nervous  substance,  the  cephalic  end  or  genu  of  the  callosum,  the 
right  cerebrum  and  bulb  must  be  cut  a  liltle  farther  cephalad  so  as  to 
clear  the  genu  entirely.  Remove  the  caudal  ends  at  a  similar  angle,  so  as 
to  present  the  surfaces  <:,  and  expo.se  the  splenium. 

§  16.  The  narrow  surfaces  d^  at  either  side  of  the  meson,  must  be 
cut  with  extreme  care.  From  PL  XXV,  especially  from  the  enlarge- 
ment of  part  of  it,  it  will  be  seen  that  at  the  bottom  of  the  mesal  inter- 
cerebral FISSURE  is  a  slight  lateral  extension  at  either  side,  the  cal- 
LOSAL  FISSURE.  In  making  the  cuts  the  object  should  be  to  remove  the 
apposed  mesal  portions  of  the  two  cerebrums  just  to  the  level  of  the  cal- 
losum and  as  far  laterad  as  the  callosal  fissures  extend  so  as  to  expose  the 
free  dorsal  surface  of  the  callosum  in  its  entire  width.  The  convexity  of 
the  tracer  may  be  used  to  advantage  in  lifting  from  the  callosum  the 
overhanging  edges,  and  these  may  be  more  safely  trimmed  afterward. 

a.  The  oblique  narrow  surfaces  e  and/need  no  special  directions  ; 
but  even  when  tliey  are  cut,  in  order  to  see  between  the  cephalic  ends  of 
the  cerebrums  it  will  be  necessary  to  divaricate  these  slightly  and  to 
remove  the  arachnoid  and  pia,  perhaps  even  a  slice  of  the  cortex  at  either 
side. 

?  17.  Labeling  the  Bi'ain.—V pon  a  bit  of  paper  as  long  as  the  greatest  width  of  the 
cerebrum  and  about  half  as  wide,  write  zvii/t  pencil  or  India  iniz  (common  writing  ink  is 
washed  out  by  alcohol)  your  name,  the  number  of  the  practicum  section  (thus  Pr.  II)  and 
the  number  of  the  window  (thus,  W.  VII).  With  a  small  pin  at  either  end  attach  it  across 
the  brain  about  in  the  position  of  the  word  cerebrum  in  PI.  XVIII. 


Practicum   VIII.      The    Encephalic  Segments.  53 

S  i8.  Study  of  the  Eiiceplialic  Segments. — Refer  to  tlie  leclure  in 
wliich  the  segmental  constimtion  of  the  brain  is  presented  as  a  funda- 
mental conception  of  the  organ. 

S  19.  So  far  as  possible  each  student  should  make  enlarged  drawings 
of  the  following  preparations.  They  should  be  kept  wet  as  directed  in 
the  initial  Caution. 

§  20.  Frog''  s  Brain^  entire^  exposed  by  removing  parts  of  the  head  on 
either  side. — The  dark  disk  at  the  side  of  the  head  is  the  tympanodisk 
{7)iembrnna  tympani),  which  in  this  animal  is  at  the  level  of  the  rest  of 
the  skin  since  there  is  no  ectal  ear  ;  Pract.  VI,  §  29. 

a.  Recall  what  was  said  in  the  lecture  as  to  the  e.Kceptional  mesal 
fusion  of  the  olfactory  bulbs  in  the  tailless  Amphibia  (frogs  and  toads). 

b.  The  real  conaritim  is  attached  to  the  cranium  and  was  removed 
therewith  ;  the  dark  mesal  mass  that  might  be  taken  for  it  is  a  plexus. 
The  caudal  region  of  this  brain  is  obscured  by  the  metatela  ;  see  §  21. 

§21.  Second  Frog^ s  Brain.,  Lacking  the  Metatela. — Only  the  caudal 
half  of  this  need  be  drawn,  showing  the  sides  and  floor  of  the  large  tri- 
angular cavity,  metacgelE  (corresponding  to  the  greater  part  of  what  is 
commonh-  called  the  "fourth  ventricle")  and  the  narrow  cerebellum 
which  was  hidden  in  the  other  specimen  by  a  cephalic  protrusion  of  the 
metatela. 

§22.  Dissected  Sheep's  Brains^  such  as  are  Represented  in  Plates 
XX-XXII. — -The  descriptions  of  these  figures  should  be  studied  carefully 
in  advance.  The  drawings  should  be  twice  the  natural  diameter  of  the 
specimens  and  should  represent  them  rather  than  mere  copies  of  the  cor- 
responding figures. 

§23.  After  the  outlines  of  the  dorsal  aspect  (PI.  XXII)  are  made 
satisfactorily  the  surfaces  may  be  distinguished  as  follows  : 

a.  The  cut  or  artifical  surfaces  may  be  left  blank,  or  the  oblique 
ones  shaded  slightly. 

b.  The  natural  surfaces  that  were  covered  by  pia  may  be  colored 
red. 

c.  The  other  natural  surfaces  are  covered  by  the  endyma,  which 
lines  the  cavities  and  may  be  colored  yellow,  £•.  ^.,'the  caudatum,  its 
CAPUT  and  cauda,  and  the  habena  just  at  the  side  of  the  mesal  diaccELE. 

d.  A  sharp  red  line  may  be  employed  to  indicate  the  cut  edge  of  a 
pial  or  ectal  surface,  e.  g..,  at  the  left  of  the  cerebrum. 

e.  A  yellow  line  may  represent  the  cut  edge  of  an  endymal  or  ental 
surface,  e.  o-. ,  along  the  lateral  margin  of  the  caudatum. 

f.  Where  the  pia  and  endymal  have  been  in  contact  and  have  been 
cut  or  torn  away  leaving  a  sharp  or  ragged  edge  of  membrane,  a  ripa,  e. 
g. ,  there  should  be  parallel  red  and  yellow  lines. 

g.  The  cerebral  and  cerebellar  cortex  may  be  indicated  by  a  slight 
shading  or  b\-  a  more  appropriate  gray  color. 


PRACTICUM  IX.     THE  MESAL  ASPECT  OF  THE  SHEEP'S  BRAIN. 

PLATES    REQUIRED,    XXIII,  XXV. 


S  I  Inevitable  Imperfection  of  the  Specimens.  — -An  absolutely  perfect 
condition  of  both  mesal  aspects  of  a  medisected  brain  could  only  result 
from  the  combination  of  tlie  following  conditions  : 

A.  The  brain  was  normal. 

B.  It  was  hardened  with  neither  deflection  of  the  long  axis  nor  tilt- 
ing of  the  cerebellum  to  one  side. 

C.  It  was  divided  accurately  upon  the  meson  throughout  its  entire 
length  and  height. 

a.  Reference  to  Plates  XXIII,  XXIV,  XXV,  will  show  that  the 
chances  are  against  the  passage  of  the  knife  exactly  between  the  apposed 
surfaces  without  cutting  either,  and  against  the  cutting  of  azygous  parts 
precisely  at  the  meson.  For  example,  in  PI.  XXV,  near  the  center,  is  a 
dorso-ventra)  dark  area  representing  a  narrow  cavity,  the  pseudoccELE, 
bounded  at  either  side  by  a  thin  lamina,  the  hemiseptum.  The  actual 
parts  are  onlv  one-fourth  the  dimensions  in  the  lower  figure.  If,  instead 
of  bisecting  the  pseudocoele  the  knife  should  pass  a  very  slight  distance 
to  the  right  or  left  of  the  meson,  then,  at  that  point,  in  place  of  two  nat- 
ural surfaces  would  be  two  cut  surfaces  ;  and  if  it  should  pass  still  farther 
laterad,  it  would  open  the  cavity  at  the  other  side  of  the  hemiseptum  so 
that  one-half  of  the  brain  would  present  a  surface  and  the  other  a  cavity; 
this  would  be  confusing  enough,  yet  it  is  only  one  of  many  possible  and 
even  probable  conditions. 

b.  Indeed  the  happy  combination  indicated  in  ?  i  has  not  occurred  in  the  writer's 
experience.  He  has  found  that  practically  the  best  plan  has  been  to  cut  a  trifle  laterad  of 
the  meson,  preferably  to  the  left,  then  to  shave  ofi"  from  the  right  half  the  parts  of  the 
left  that  adheres  to  it ;  in  other  words,  one-half  of  the  brain  is  sacrificed  to  the  other. 

c.  Even  with  this  method  the  result  is  uncertain  ;  the  specimens  submitted  to  the 
class  at  this  practicum  have  been  selected  from  several  hundred.  They  must  be  studied  in 
turn  by  all  the  members  of  the  class  ;  hence  they  should  be  handled  with  great  care.  In 
lifting  place  the  fingers  and  thumb  upon  the  ventral  and  dorsal  surfaces  respectively  ; 
make  no  pressure  upon  the  mesal  parts  ;  keep  them,  andindeed  the  entire  specimen,  con- 
stantty  wet  with  alcohot. 

%  2.  The  good  meson  may  be  either  right  or  left,  preferably  the 
former  for  readier  comparison  with  the  wall-maps  of  the  sheep,  cat, 
human  and  chimpanzee  brains  and  with  the  figures.  But  in  addition 
there  are  a  right  and  a  left  half-brain,  with  poor  mesons.  Even  if  they 
are  not  really  mates,  i.  e.,  halves  of  the  same  brain,  they  will  serve  cer- 
tain purposes  in  this  practicum,  and  may  be  handled  more  freely,  but  still 
with  care. 

§3.  Appose  the  mesons  of  the  two  half-brains,  and  review  the 
base  or  ventral  aspect  in  comparison  with  Plates  XIX  and  XX.  The 
HYPOPHYSIS  has  been  removed  ;  in  the  midst  of  the  TUBER,  the  slight 
elevation  to  which  it  was  attached,  is  a  mesal  orifice,  the  lura,  resulting 
from  cutting  or  tearing  off  the  stem  of  the  hypophysis. 

The  lura  leads  dorsad  into  a  shallow  depression  in  the  mesal  surface, 
(PI.  XXIII,  diacoele),  indistinct  in  one,  perhaps  both,  of  the  poor  half- 
brains,  but  more  or  less  distinct  in  the  good  preparation.  Trace  this 
depres.sion   dorsad    and    then    caudad,  and    note   that  in  the  region  of  the 


Praetieum    IX.      The    Encephalic  Segments.  SS 

GEMiNA,  the  MESENCEPHAL,  its  depth,  /.  e.^  its  lateral  diameter,  is  some- 
what greater,  while  its  dorso-veiitral  diameter  is  less  ;  it  is  thus  a  furrow, 
and  of  course  with  its  opposite  constitutes  a  sub-cylindrical  tube,  the 
MESOCCELE,  often  called  the  aqueduct.  .Its  relation  to  the  gemina  ma)-  be 
seen  also  in  the  transection  of  this  region,  corresponding  with  the  line 
D-D  across  PI.  XXIII. 

§4.  The  detailed  stud}- of  the  encephalic  meson  may  conveniently 
follow  this  order  : 

a.  Recognizing  the  larger  masses. 

b.  Recognizing  the  six  segments. 

c.  Determining  the  continuity  of  the  mesal  cavities. 

d.  Determining  the  complete  circumscription  of  the  cavities. 

e.  Discriminating  between  the  several  kinds  of  surfaces  and  cut 
edges. 

f.  Drawing  the  specimen  in  hand. 

g.  Comparing  the  parts  visible  at  the  meson  with  the  same  as  seen 
in  transections  ;  to  be  done  at  Pract.  XI. 

h.  Comparing  the  mesal  aspect  of  the  sheep's  brain  with  that  of  man 
and  other  animals. 

§  5.     Promment   Pai-ts. — At    Pract.  VIII  were  seen  the  cerebrum, 

CEREBELLUM,     OLFACTORY    BULB,  PONS,    CHIASMA    and    HYPOPHYSIS  ;    also, 

upon  removal  of  the  dorsal  part  of  the  cerebrum,  the  mesal  part  of  the 
CALLOSUM. 

§6.  The  Segments. — a.  The  entire  cerebellum,  pons  and  preoblon- 
gata  (cephalic  part  of  the  oblongata)  constitute  the  epencephal. 

b.  The  rest  of  the  oblongata,  postoblongata,  is  the  metencephal. 

c.  The  MESENCEPHAL  includes  the  crura,  postgeminum  and  pregem- 
inum. 

d.  The  DIENCEPHAL  is  represented  by  the  Inpophysis  and  adjacent 
parts,  the  conarium  and  adjacent  parts,  and  the  medicommissure  connect- 
ing two  considerable  masses,  the  thalami,  seen  in  PI.  XXII. 

e.  The  cerebrum  constitutes  the  prosencephal. 

f.  The  Rhiiiencephal  comprises  the  olfactory  bulbs  and  their  crura  ; 
also  parts  of  the  olfactory  tracts,  of  the  precommissure  and  of  the  aula 
which  are  commonly  regarded  as  constituents  of  the  cerebrum. 

g.  The  segmental  constitution  of  the  brain  is  discussed  in  the  lectures  on  the  develop- 
ment of  the  organ  :  See  Anat.  Teclinology,  p.  405  and  Handbooli,  -VIII,  p.  114  and  IX,  p. 
loi,  for  admissions  of  the  modification  of  the  writer's  views  upon  the  subject. 

§7.  The  Mesal  Cavities. — These  are  indicated  on  PI.  XXIII  by  the 
darkly  shaded  area  ;  their  forms  are  more  fully  exhibited  in  Handbook 
Fig.  4703. 

a.  The  cavity  of  the  myel  is  a  slight,  cylindrical  canal,  the  myrl- 
OCCELE  (not  named  in  PI.  XXIII). 

b.  The  METACCELE  is  slightly  higher  and  (as  will  be  seen  later)  con- 
siderably wider. 

c.  The  EPiCCELE  has  a  marked  dorsal  extension  into  the  cerebellum. 

d.  The  MESOCCELE  is  tubular  but  curved  and  somewhat  irregular. 

e.  The  diaccele,  surrounding  the  medicommissure,  is  irregular, 
narrow,  but  extensive  in  the  other  directions. 

f.  In  this  view  of  the  brain  the  prosoccele  is  represented  only  by 
the  AULA,  a  small  space  cephalad  of  the  medicommissure,  at  the  dorsal 
end  of  the  slight,  curved  furrow  named  aulix.  But  if  the  preparation  be 
held  obliquely  there  will  be  seen  a  narrow  passage,  the  porta,  leading 
latero-cephalad  into  the  paraccele  (lateral  ventricle)  of  tliat  side  ;  this 
will  be  exposed  at  the  next  praclicnm. 


56  Praetieum  IX.    The   Coelian  Parietes.  \ 

g.  Small  as  is  the  aula  a  part  of  it  constitutes  the  mesal  division  of 
the  Rhmoccele,  the  larger  portions  being  hidden  within  the  olfactory 
bulbs. 

§8.  Ccelian  Parietes. — The  walls  of  the  brain  cavities,  ventral,  lat- 
eral, and  dorsal,  are  comparable  with  floors,  sides  and  7'oofs. 

a.  Beginning  with  the  mesoccele  the  crura  constitute  a  substantial 
floor.  At  the  meson  the  roof  is  of  moderate  thickness,  but  at  either  side 
the  geminal  lobes  are  massive. 

§9.  The  preoblongata  is  reinforced  by  the  pons.  Part  of  the  epiccele 
is  a  dorso-ventral  extension  into  the  massive  cerebellum.  But  if  the  cer- 
ebellum be  tilted  slightly  laterad  (more  freely  is  the  extra  half-brain),  its 
cephalic  part  will  be  seen  to  overhang  a  thin  lamina,  the  lingula,  which 
is  the  true  roof  of  the  cephalic  part  of  the  epiccele,  and  which  is  contin- 
uous with  the  VALVULA,  a  similar  thin  portion  of  the  mesoccelian  roof. 

§  10.  The  floor  of  the  metacoele  is  obvioiis.  Its  roof  is  even  thinner 
than  the  lingula.  If  the  cerebellum  of  the  extra  half-brain  be  tilted 
latero-cephalad  there  will  appear  a  membranous  sheet,  continuous 
caudad  with  the  roof  of  the  myelocoele,  and  cephalad  attached  to 
the  cerebellum  at  some  point  on  the  caudal  wall  of  the  dorsal  extension 
of  the  epiccele.  This  metateLA  consists  of  the  pia.  which  follows  the 
ectal  contour  of  the  parts,  i;nited  with  the  endyma  that  lines  the  cav- 
ities. 

§11.  The  diacoelian  floor  is  variously  constituted.  The  tuber,  to 
which  the  hypophysis  is  attached,  is  thin  ;  but  caudad  is  the  prominent 
albicans,  and  cephalad  the  chiasma  ;  dorsad  of  the  chiasma  is  another 
thin  portion,  the  terma  {lamina  tertninalis).  The  terma  is  so  thin  that 
even  when  it  has  escaped  injurv  in  the  medisection  of  the  brain  it  may 
not  be  readily  recognized  unless  three  points  are  borne  in  mind  :  i.  Its 
direction  is  dorso-caudad  ;  2.  It  starts  from  the  dorsal  surface  of  the 
chiasma  rather  nearer  its  cephalic  margin  than  is  represented  in  PI. 
XXIII  ;  3.  Dorsally  it  is  continuous  with  a  distinctly  oval  thickening,  the 
PRECOMMissuRE,  opposite  the  middle  of  the  medicommissure. 

§  12.  The  diacoelian  roof  is  irregular  in  direction  and  varions  in  com- 
position, and  will  be  most  easily  traced  from  the  end  next  the  mesence- 
phal.  The  conarium  has  already  been  recognized  (§6)  between  the  pre- 
geminumand  the  splenium,  the  caudal  end  of  the  callosum.  By  gently 
moving  its  caudal  end,  its  ventro-cephalic  angle  will  be  found  to  be  con- 
tinuous with  the  mesoccelian  roof  b}'  a  curved  and  corrugated  lamina,  the 
POSTCOMMissuRE.  Just  dorsad  of  this  is  a  short  triangular  recess  in  the 
substance  of  the  conarium.  If  the  parts  are  examined  closely,  especially 
with  a  lens,  the  opposite  boundary  of  this  recess  will  be  recognized  as  a 
subcyliudrical  lamina,  the  supracommissure.  Just  dorsad  of  this  will 
be  seen  a  membrane,  the  diatela,  represented  in  PI.  XXIII  by  a  white 
line.  Really  the  ventral  ental  surface  of  the  diatela  presents  a  series  of 
ridges  constituting  a  fringe,  the  diaplexus.  Traced  caudad  the  diatela 
will  be  found  to  form  a  sort  of  pouch  on  the  dorsal  side  of  the  conarium  ; 
it  appears  to  be  attached  near  its  tip,  as  shown  in  PI.  XXIII,  but  ma\' 
commonly  be  detached  nearly  or  quite  to  the  supracommissure.  Traced 
cephalad  the  diatela  will  be  found  loosely  attached  to  the  parts  dorsad  of 
it  until,  at  a  point  dorsad  of  the  middle  of  the  medicommissure,  it  is  no 
longer  separable  easily. 

§13.  The  Lateral  Boundary  of  the  Dorsal  part  of  the  Diac^sle. — 
Excepting,  perhaps,  the  metacoele  the  cavities  so  far  inspected  present  not 


Practieum  IX.    Coelian  Circumscription.  S7 

only  floors  and  roofs  but  definite  and  continuous  sides.  But  the  middle 
portion  of  the  dorsal  part  of  the  diaccele  seems,  at  first  sight,  to  extend 
laterad  indefinitely  upon  the  dorsum  of  the  thalamus,  and  if  the  student 
is  already  aware  that  each  cerebrum  contains  a  cavity,  the  paraccele 
(lateral  ventricle),  he  may  well  infer  that  here  is  a  direct  communication 
therewith. 

Since  this  idea  is  rank  morphologic  heresy,  the  parts  should  be 
examined  very  carefully. 

§  14.  Hold  the  less  perfect  extra  half-brain  in  the  left  hand  ;  press 
the  left  thumb  firmly  against  the  mesal  surface  of  the  mesocoelian  floor 
(PI.  XXIII  crura) ;  place  the  tip  of  the  scalpel  handle  (or  similar  smooth, 
dull  instrument  about  i  cm.  wide)  ventrad  of  the  middle  of  the  diatela, 
and  press  it  against  the  parts  dorsad  of  it  ;  increase  the  pressure  very  cau- 
tiously until  it  can  be  seen  that,  at  the  distance  of  2-3  mm.  from  the 
meson,  the  diatela  unites  with  the  dorsum  of  the  thalamus  and  the  diaccele 
is  there  limited ;  compare  Plates  XXII  and  XXV. 

a.  But  when  this  line  of  attachment  is  traced  cephalad  it  will  be 
found  to  cease  dorsad  of  the  cephalic  slope  of  the  medicommissure.  From 
this  point  cephalo-ventrad  nearly  to  the  level  of  the  precommissure  there 
is  evidently  a  passage  extending  laterad  ;  thi.'^  is  the  PORTA,  (foramen  of 
Monro)  and  the  cavity  into  which  it  leads  is  the  paraccELE  (lateral  ven- 
tricle) to  be  examined  later.  The  mesal  cavity  between  the  two  ]3ortas  is 
the  AULA,  the  small  mesal  division  of  the  prosocoele,  the  general  cavit}' 
of  the  prosencephal  ;  see  Handbook  Fig.  4703.  The  roof  of  the  aula  is 
not  the  diatela  but  the  mesal  part  of  the  fornix, /cw.  in  PI.  XXIII,  to  be 
examined  later. 

§  15.  The  Crista. — ^Just  dorsad  of  the  precommissure  is  a  slight 
rounded  elevation,  the  crista.  If  the  plane  of  section  has  coincided 
with  the  meson  it  will  appear  as  in  PI.  XXIII  ;  but  it  has  passed  sinistrad 
of  the  meson,  with  a  right  half  it  may  remain  entire. 

§  16.  The  Habena. — Just  cephalad  of  the  conarium  is  a  low  ridge, 
widest  and  most  distinct  caudad,  but  becoming  both  narrowt-r  and  fainter 
it  extends  dorsad,  cephalad  and  laterad  along  the  dorsal  slope  of  the 
thalamus  ;  this  is  the  habena.  If  the  supracommissure  is  examined 
with  the  lens  it  will  be  seen  to  be  a  transverse  band  connecting  across  the 
meson  the  dorsal  parts  of  the  caudal  ends  of  the  two  habenas. 

§  17.  Coeliaii  Circumscription  and  Endymal  Continuity. — From  the 
examination  just  concluded  it  ina)-  be  seen  that  the  mesal  series  of  cavi- 
ties is  circumscribed  by  continuous  parietes,  floors,  end,  roof  and  sides, 
covered  by  the  lining  endyma  ;  also  that  this  circumscription  would  still 
be  maintained  even  were  most  of  the  eerebrtim  and  cerebellum  removed. 

§18.  The  Surfaces  that  Appear  upon  the  Mesal  Aspect. — The  two 
kinds  are  natural^  and  artificinl  ox  cut  The  roof  of  the  mesocoele  furn- 
ishes an  example  of  each.  The  shaded  area  represents  the  mesal  slope  of 
a  lateral  .convexity,  the  right  half  of  the  pregeminum.  The  unshaded 
area  just  dorsad  of  the  mesocoeie  represents  the  depressed  roof  between 
the  lateral  masses,  which  was  divided  by  the  medisection.  All  the  other 
unshaded  areas  represent  cut  surfaces;  e.  g.,  cerebellum,  medicommis- 
sure, hypophysis,  etc.  Certain  jiarts  that  are  distinctly  fibrous  are  indi- 
cated by  dots,  e.  g.,  the  callosum,  pons,  chiasnia. 

The  divisions  of  the  cerebellum  ifoHums)  are  not  shown,  and  neither  here  nor  else, 
where  has  the  cinerea  (gray  nervous  substance)  been  distinguished  from  the  alba,  except- 
ing that  the  fibrous  parts  indicated  by  dots  are  of  course  alba  (white  nervous  substance)- 
The  color  difference  between   the   alba  and   cinerea  does  not  appear  distinctly  upon  alco- 


58  PracLicum    IX.     Endymal   Continuity. 

holic  specimens  ;  the  distinction  of  the  two  kinds  of  substance  may  be  observed  to  better 
advantage  upon  brains  hardened  in  formalin  or  in  potassium  dichromate,  to  be  exam- 
ined at  Pr.  XI. 

§  19.  With  one  exception  (to  be  considered  presently)  the  nat.ural  or 
uncut  surfaces  are  of  two  kinds  :  endymal^  enlal  or  entocoelian,  and  pia/, 
ectal  or  ectocoelian. 

a.  The  first  includes  all  the  true  encephalic  cavities  whose  circuni- 
scription  has  been  traced  already  (S8j.  The  lining  membrane  is  smooth 
and  in  certain  lights  sliining.  The  difference  between  the  endymal  sur- 
face and  a  cut  surface  may  be  seen  b)-  comparing  the  mediconimissure 
with  the  slighth'  depressed  area  surrounding  it. 

b.  The  triangular,  shaded  area  just  ventrad  of  the  cephalic  three- 
fifths  of  the  callosum  represents  the  hemiseptum,  the  lateral  wall  of  the 
narrow  mesal  cavity,  pseudocoele  (fifth  ventricle).  This  cavity  has  no  nor- 
mal communication  with  the  true  encephalic  cavities,  and  is  cut  off  from 
the  ectal,  pial  surfaces  by  the  pia  which  extends  from  the  rostrum,  the 
tip  of  the  callosum,  to  the  crista  ;  so  far  as  the  writer  is  aware  no  mem- 
brane of  any  kind  has  been  recognized  upon  the  surface. 

c.  All  ihe  other  natural  surfaces  are  covered  by  pia.  For  its  char- 
acter and  relations  see  Pract.  VIII,  §8  If  time  permits  it  may  be  traced 
over  all  tiie  parts,  in  close  contact  with  them. 

§20.  The  Cut  Edges  of  Metnbranes. — The  cut  edge  of  the  endyma 
is  indicated  on  PI.  XXIII  by  the  continuous  black  line  at  the  ental  margin 
of  all  the  divided  parietes.  So  much  of  the  endyma,  however,  as  consti- 
tutes the  ental  layer  of  the  diatela  is  represented  by  the  corresponding 
halt  of  the  light  line.  The  pial  edge  corresponds,  for  the  most  part,  to 
the  ectal  margin  of  all  the  divided  parietes.  In  the  metatela  it  and  the 
endyma  are  practically  one.  On  the  lingula,  valvula  and  terma  it  is  not 
easily  separable  without  tearing  those  attenuated  parts.  Opposite  the 
middle  of  the  medicommissure,  instead  of  following  the  line  of  the  im- 
mediate roof  of  the  cavity,  it  is  deflected  to  the  tip  of  the  callosum,  the 
rostrum,  passes  over  the  genu,  along  the  dorsal  side  of  the  callosum, 
dipping  into  the  callosal  fissure.  It  then  passes  about  the  splenium  to  the 
ventral  side  of  the  fornix  [fern.)  continuing  as  far  cephalad  as  the  point 
where  the  diatela  cea.ses  to  be  attached,  the  dorsal  end  of  the  porta  (§  14, 
a).  Here  it  turns  upon  itself,  and  becomes  united  with  the  endyma  to 
form  tlie  diatela. 

§  21.  The  Velum. — From  the  foregoing  it  will  be  seen  that  between 
the  diaccele  and  the  ventral  surface  of  the  fornix  and  splenium  there  are 
two  layers  of  pia,  continuous  cephalad  but  diverging  caudad.  One  be- 
longs to  the  diencephal,  the  other  to  the  overhanging  cerebrum  ;  the  two 
layers  of  pia,  with  the  vessels  between  them,  are  commonly  called  the 
VELUM,  but  it  must  not  be  forgotten  that  the  closer  junction  of  the  ven- 
tral laver  with  the  endyma  constitutes  the  diatela.  The  relations  will  be 
clearer  when  PI.  XXV  is  studied. 

§  22.  Drawirtg  the  Mesal  Aspect. — The  specimen  in  hand  is  to  be 
drawn,  enlarged  two  diameters.  PI.  XXIII  and  the  foregoing  text  maybe 
used  for  reference  and  comparison,  but  the  figure  is  not  to  be  copied.  The 
following  method  will  be  found  convenient  : 

a.  Support  the  specimen  in  a  small  dish  or  upon  a  bed  of  cotton, 
(or  cloth,  or  Japanese  napkin)  so  that  the  meson  is  nearly  at  an  angle  of 
45°  with  the  table  and  thus  nearly  at  a  right  angle  with  the  line  of  vision. 
L,et  the  length  of  the  callosum  be  nearly  horizontal. 

/;.     Keep  the  specimen  wet  with  alcohol.     If  by  inadvertence  it  act- 


Practieum   IX.     Drawing    the    Meson.  59 

ually   becomes  dry,  call  the  assistant's  attention    to  it,  and  immerse  in 
water  for  a  few  moments. 

c.  Make  four  light  horizontal  and  parallel  lines  twice  the  length  of 
the  brain,  coinciding  respectively  with  the  dorsal  convexity  of  the  cere- 
brum, the  ventral  convexity  of  the  pons,  the  dorsal  margin  of  the  cal- 
losum  and  the  ventral  margin  of  the  medicommissure.  At  right  angles 
to  these  make  three  perpendicular  lines  coinciding  respectively  with  the 
cephalic  convexity  of  the  cerebrum,  the  caudal  convexity  of  the  cerebel- 
lum and  the  caudal  margin  of  the  medicommissure.  The  intermediate 
line  will  be  very  nearly  in  the  middle  of  the  length  of  the  brain.  By 
measuring  with  the  dividers  double  the  distance  of  any  point  from  the 
places  of  intersection  considerable  accuracy  may  be  attained. 

§  23.  The  cavities  should  be  outlined  first  and  fully  their  natural 
dimensions,  twice  enlarged  ;  that  is,  since  these  spaces  at  most  are  rather 
slight,  while  the  encompassing  masses  are  considerable,  the  latter  may 
be  diminished  with  less  risk  of  obscurity  in  the  drawing. 

a.  The  callosum  and  medicommissure  should  be  outlined  first  ; 
although  often  nearly  circular,  as  in  PI.  XXIII,  the  latter  is  by  no  means 
always  so,  being  sometimes  oval  or  elliptical. 

b.  Next  the  floor  of  the  mesal  cavities  ;  if  as  is  commonly  the  case, 
the  hypophysis  has  been  removed,  it  may  be  omitted  or  copied  from  the 
figure. 

c.  Then  the  roof  of  the  mesoccele  ;  the  ental  line  should  be  sharp 
and  clear  to  represent  the  endyma,  the  ectal  line  of  the  cut  surface  not 
quite  so  heavy,  but  distinct,  to  represent  the  pia.  The  convex  outline  of 
the  geminums  should  be  light,  and  the  intervening  pial  surface  indicated 
later  by  light  shading.  If  the  three  kinds  of  sui faces — cut,  pial  and  en- 
dymal — are  not  at  first  easily  discriminated,  hold  the  specimen  so  that  the 
light  strikes  successively  at  diff^erent  angles. 

d.  Next  the  thin  lamina,  valvnla  and  lingula,  roofing  in  the  com- 
municating portions  of  the  mesoccele  and  epicoele.  Observe  the  caution 
given  in  §  9  and  get  these  parts  from  the  less  perfect  specimen  ;  their 
precise  thickness  may  not  be  worth  taking  time  to  ascertain,  but  the  two 
lines  representing  the  pial  and  endymal  coats  of  the  lingula  should  be 
about  as  near  together  as  they  can  be  and  yet  be  distinguishable. 

e.  The  myeloccele  (central  canal  of  the  myel)  is  seldom  visible  for 
any  distance  in  medisected  brains  unless  special  pains  have  been  taken  to 
expose  it  ;  if  the  section  has  passed  to  the  side  opposite  that  to  which  the 
specimen  belongs,  the  continuation  of  the  metacoele  with  the  myeloccele 
may  sometimes  be  seen  as  a  funnel-shaped  orifice  by  looking  obliquely 
latero-caudad  at  the  extremity  of  the  metaccele  ;  the  presumed  continua- 
tion may  then  be  represented  by  two  parallel,  interrupted  lines. 

f.  The  membranous  metatela  (§  10)  is  shown  in  PL  XXIII  as  a  sin- 
gle line  representing  the  union  of  the  endyma  with  the  pia  which  is 
reflected  from  the  dorsum  of  the  myel  upon  the  ventral  surface  of  the 
overhanging  cerebellum  ;  the  place  of  reflection  is  located  in  the  figure  at 
the  angle  between  the  ventral  surface  of  the  cerebellum  and  the  dorsal 
extension  of  the  epiccele  ;  but  in  some — perhaps  most — specimens  the 
membranous  lamina  may  be  traced  for  some  distance  dorsad  of  this  angle  ; 
there  may  not  be  time  to  ascertain  the  condition  in  the  specimen,  but  an}- 
doubt  may  be  recorded. 

g.  The  dorsal  extension  of  the  epicoele  should  be  given  its  full 
width  or  even  more. 

§  24.  The  mass  of  the  cerebellum  may  now  be  outlined.  Unless 
there  is  plenty  of  time  a  single  line,  as  in  PI.  XXIII  mav  suffice.      But  if 


60  Praetieum  IX.     Drawing  the   Meson. 

there  is  opportunity  for  elaboration  later,  there  may  be  introduced  some 
of  the  foliums  between  which  the  pia  dips  in  folds  ;  the  first  outline 
might  then  represent  the  arachnoid  which,  as  seen  in  Pract.  VIII,  passes 
over  the  rimulas,  bridges  the  interval  between  the  cerebellum  and  the 
cerebrum  not  far  dorsad  of  the  pregeminum,  and  passes  from  the  caudal 
convexity  to  the  myel. 

a.  If  preferred,  as  in  PI.  XXIII,  the  cerebellum  may  be  represented 
as  if  tilted  caudad  enough  to  exhibit  more  clearly  the  interval  between  it 
and  the  cerebrum,  but  as  this  would  involve  shifting  the  oblongata  also, 
the  same  end  may  be  attained  by  diminishing  the  width  of  the  cerebel- 
lum somewhat,  or  by  reducing  the  length  of  the  cerebrum  ;  the  exacti- 
tude of  these  dimensions  is  not  essential  for  the  purpose  of  the  present 
examination. 

§  25.  The  cut  surfaces  of  the  conarium,  postcommissure  and  supra- 
commissure  may  be  outlined  next  ;  the  conarium  may  be  made  a  trifle 
smaller  than  it  should  be  in  case,  later,  room  is  lacking  between  it  and 
the  overhanging  callosum  to  show  clearly  the  diatela  as  resulting  from 
the  junction  of  the  diacoelian  endyma  and  the  ventral  layer  of  the  velum, 
and  also  tlie  dorsal  layer  of  pia  which  adheres  to  the  callosum  and  fornix 
(§20). 

a.  Besides  the  fringe-like  diaplexus  referred  to  in  §  12  there  may 
appear  the  whole  or  part  of  the  mesal  vela?'  vein  (PL XXV)  which  passes 
between  the  two  layers  of  the  velum  and  opens  into  a  blood-sinus,  the 
depression  caused  by  which  is  indicated  in  PI.  XXIII  by  the  shaded  tract, 
/,  just  caudad  of  the  splenium.  It  may  be  better  not  to  try  to  show  this 
vein. 

§  26.  The  heavy  line  representing  the  endyma  should  be  continued 
from  the  dorsal  end  of  the  porta  (at  about  the  letters yrw.)  with  slight 
undulations  to  represent  tlie  crista  and  precommissure,  to  the  chiasma 
and  so  back  to  the  tuber. 

§27.  The  ectal  or  pial  outline  of  the  parts  just  named  present  no 
serious  difficulties,  but  care  must  be  taken  to  discriminate  between  the 
mesal  cut  surface  of  the  chiasma  and  the  retreating  pial  surface  of  the 
optic  nerve.  The  terma  must  be  represented,  like  the  lingula,  by  two 
barely  separated  lines,  diverging  dorsad  at  the  precommissure.  At  or  near 
the  crista  the  pia  makes  a  sharp  turn  cephalad  to  the  rostrum  and  extends 
dorsad  of  the  callosum,  while  the  outline  of  the  fornicommissure  extends 
in  the  opposite  direction. 

§28.  The  fibrous  constitution  of  parts  like  the  callosum  and  pons 
may  be  indicated  by  dots.  In  some,  even  alcoholic,  preparations,  the  cut 
surface  of  the  cerebellum  may  present  traces  of  the  color  diflTerence  be- 
tween the  alba,  radiating  from  near  the  epiccele  as  larger  and  smaller 
branches  and  fringes,  and  the  cinerea  constituting  a  rather  thin  cortex  at 
the  periphery  of  the  foliums  ;  if  so  the  cinerea  may  be  shaded  lightly. 

§  29.  The  mass  of  the  hemicerebrum,  which  might  naturally  have 
been  drawn  first,  is  to  be  last  done,  together  with  the  olfactory  bulb.  The 
fissures  may  be  shown  as  lines,  preferably  red,  to  indicate  the  folds  of 
vascular  pia  that  dip  into  them.  Strictly,  the  callosal  fissure  also  should 
be  so  represented,  but  if  so,  just  ventrad  of  it  the  ctit  edge  of  the  pia  cross- 
ing the  meson  should  appear  as  a  narrow  black  line. 

§30.  The  Arachnoid. — Since,  as  seen  in  Pract.  VIII,  §§6,  7,  the 
arachnoid  bridgfes  the  intercerebral  fissure,  leaving  the   mesal  surface  of 


Praetieum  IX.     Comparison   with    Man.  61 

either  cerebrum  near  its  dorsal  margin,  its  cut  edge  should  be  shown  as  a 
delicate  line  along  the  curvature  ;  it  may  be  seen  more  distinctly  if  the 
specimen  be  placed  in  alcohol  or  water  deep  enough  to  just  cover  the 
meson.  The  writer  has  not  yet  traced  completely  the  arachnoid  line 
upon  a  medisected  brain. 

§  31.  Shading. — When  the  outlines  are  satisfactory  then  the  natural 
surfaces,  both  pial  and  endymal,  may  be  lightly  shaded,  the  recesses  and 
intervals  more  heavily,  approximately  as  in  PI.  XXIII.  All  the  cut 
edges  of  pia  and  endyma  sliould  be  shown  as  distinct  lines. 

§32.  Continuity  of  Membrane  Lines. — The  continuity  of  the  en- 
dyma has  been  mentioned  in  §  17  ;  the  same  is  true  of  the  pia  ;  i.  e., 
starting  from  any  point,  the  pia  may  be  traced  caudad  to  the  cut  end  of 
the  mvel  ;  then  cephalad,  and  dorsad  or  ventrad  as  the  case  may  be,  and 
again  caudad  to  the  other  margin  of  the  myel. 

§33.  Coloring. — This  endymal  and  pial  continuity  may  be  more 
readily  recognized  upon  the  drawing  if  the  cut  edges  of  the  endyma  are 
represented  by  yellow  lines  and  those  of  the  pia  by  red.  The  fissures 
also,  as  containing  folds  of  the  vascular  pia,  may  be  made  red  ;  if  so, 
the  extent  of  the  callosal  fissure  may  be  indicated  by  a  thickening  of  the 
red  line  corresponding  therewith.  The  metatela  and  diatela  will  require 
red  and  yellow  lines  in  contact. 

§  34.  Comparison  of  the  Mesal  Aspect  of  the  Sheep''  s  Brain  with  that 
of  Man. — For  this  purpose  there  should  be  actual  specimens,  prepared  in 
the  same  way  as  the  sheep  half-brains  ;  but  the  difficulties  presented  by 
the  sheep  brain  are  far  greater  with  the  human  ;  indeed  the  writer  has 
never  seen  an  even  approxiinately  perfect  preparation.  The  best  speci- 
mens in  the  museum  are  reprsented  in  Handbook  figures  4684,  47 11  and 

4718  ;  copies  of  the  first  and  third  are  supplied  to  the  class  ;  see  also  the 
wall-map  enlargement  of  the  first. 

§  35.  The  student  should  note  for  himself,  as  concisely  as  possible, 
the  more  obvious  differences  in  proportion,  relative  position,  form,  etc., 
beginning  with  those  of  a  more  general  character.  The  fissures  need  not 
be  considered. 

The  following  differences  might  escape  notice  from  the  imperfections 
of  the  figures,  but  the\'  merit  attention  as  relating  to  known  or  presumed 
peculiarities  of  the  human  brain,  shared  in  some  cases,  perhaps,  by  those 
of  the  apes  : 

a.  The  interruption  of  the  metatela,  constituting  the  metapore  ; 
this  is  considered  in   the  description  of  the  figure  ;  see  Handbook  Fig. 

4719  and  Vol.  IX,  Fig.  422. 

b.  The  presence,  on  the  dorsal  side  of  the  lingula  (§  9  )  of  three  or 
four  ridges,  indicated  in  the  figure  by  the  serrated  outline  ;  see  Handbook 
Fig.  4719  and  Vol.  IX,  Fig.  422. 

c.  The  smallness  of  the  medicommisstire  in  man  ;  most  of  it  is  cov- 
ered by  the  word  diencephal ;  see  Figs.  47 11  and  4718. 

d.  The  extension  of  the  rostrum  of  the  callosum  so  as  to  be  contin- 
uous with  the  terma  just  dorsad  of  the  precommissure,  thus  completely 
circumscribing  the  pseudocoele  by  nervous  tissue  ;  this  is  clear  in  Figs. 
47 1 1  and  4718,  but  in  Fig.  4684  the  extension,  copula.,  is  obscured  by 
names. 

e.  The  olfactory  bulb  and  cms  are  hidden  by  the  depth  of  shading, 
but  their  smallness  mav  be  seen  in  Figs.  4718  and  4689. 

f     In  man  there  are  two  albicantia,  as  seen  in  Figs.  4689,  4712  and 


62  Praetieum   IX.     Comparison   with    Man. 

4738.     Hence  a  medisection  passes  between,  and  the  retreating  convexity 
of  the  right  one  should  appear  as  shading,  as  in  Fig.  471 1. 

g.  '  Between  the  dorsal  portions  of  the  two  hemicerebrums  projects  a 
fold  of  dura,  the/a/,r.  Fig.  47 11.  This  carries  before  it  the  arachnoid  and 
hence  the  cut  edges  of  the  latter  follow  the  ental  margin  of  the  falx  in- 
stead of  lying  near  the  dorsal  margin  ;  it  is  faintly  indicated  in  Fig.  4684 
by  the  interrupted  line  J. 


PRACTICUM  X  :  DISSECTION  OF  THE  SHEEP'S  BRAIN. 

PLATES    REQUIRED  :    XVIII-XXV. 

§  I.  At  the  best  the  time  available  at  two  ordinary  practicums  is 
altogether  inadequate  for  the  demonstration  and  comprehension  of  the 
macroscopic  structure  of  the  brain.  All  the  exercises  should  be  re- 
peated wheu  opportunity  offers.  Upon  the  transections  many  hours  may 
be  profitably  spent. 

§2.  For  reference  during  this  practicum  and  the  next  there  should 
be  a  good  mesal  aspect,  as  in  PI.  XXIII,  and  preparations  such  as  are 
shown  in  Plates  XX-XXII  and  XXIV. 

a.  If  two  brains  are  available  one  may  be  dissected  as  directed  below  and  the  other 
transected  at  the  levels  indicated  by  the  dorso-ventral  lines  A — G  upon  PI.  XXIII,  and 
elsewhere  if  desired. 

b.  If  two  students  are  working  together  and  have  each  a  brain,  one  may  be  used  for 
the  transections  ;  of  the  second  brain  the  left  paracoele  may  be  exposed  by  one  and  the 
right  by  the  other  ;  the  non-dissector  should  watch  and  cooperate. 

c.  With  modifications  that  need  not  be  specified  the  following  directions  apply  to 
either  half  of  a  medisected  brain. 

d.  Wherever  the  tracer  is  mentioned  iu  this  practicum  the  syringotome  would  be 
preferable  ;  Anat.  Technology,  Fig,  15  ;  Ref  Handbook,  VIII,  Fig.  4880. 

§3.  The  Cerebellum. — From  this  may  have  been  removed  already 
either  the  dorsal  portion  or  the  cephalic  and  caudal  convexities,  or  all 
three  (Pract.  VIII,  §§  11,12).  On  the  lateral  aspect,  overhanging  the  pons 
note  several  series  of  foliums.  With  the  tracer  push  them  dorsad.  They 
will  easily  break  away  from  a  stem  of  alba  which  is  continuous  ventrad 
with  the  pons  and  extends  dorso-caudad  into  the  central  alba  of  the  cere- 
bellum. This  stem  is  the  MEDIPEDUNCLE,  designated  in  PI.  XXI 
by  7,  but  the  number  is  very  indistinct. 

§4.  The  Metatela. — Depress  the  postoblongata  and  push  the  caudal 
part  of  the  cerebellum  dorso-cephalad.  If  this  is  done  cautiously  and  the 
brain  has  been  well  prepared,  there  will  be  seen  the  metatela,  the  mem- 
branous roof  or  the  metacoele,  Pract.  IX,  §  10,  §  23  y^  But  often  it 
adheres  to  the  cerebellum  so  as  to  be  torn  more  or  less. 

§  5.  The  Lingula  and  Valvula. — These  are  to  be  exposed  by  tilting 
the  cephalic  part  of  the  cerebellum  caudad,  Pract.  IX,  §9,  and  23,  d ; 
they  too  may  be  torn  in  the  process  ;  but  if  now  the  cerebellum  be  cut  off 
almost  at  the  level  of  the  oblongata  the  entire  metepieoele  (fourth  ventri- 
cle) will  be  exposed,  and  by  blowing  from  its  caudal  portion  the  lingula 
and  valvula  may  be  demonstrated  satisfactorily.  There  may  also  be  seen 
the  apex  of  the  metacoele  where  it  narrows  to  become  continuous  with  the 
myelocoele  ;  also  the  lateral  extensions  of  the  cavity  referred  to  in  §  7,  a. 

§6.  The  Other  Peduncles. — The  prominent  ridges  at  either  side  of 
the  valvula  are  the  prepeduncles,  connecting  the  cerebellum  with  the 
geminums.  The  postpeduncles,  extending  ventrad  and  caudad  to  the 
oblongata,  are  not  distinct  in  the  sheep  ;  see  Handbook  Fig.  4721. 
The  GEMINUMS  have  been  seen  in  Pract.  VIII,  PI.  XXII.  Sometimes  on 
one  or  both  sides  there  remains  the  slender  trochlearis  nerve  (PI. 
XXII)  meeting  its  opposite  in  tiie  valvula. 

§7.  The  Flocculus. — Of  the  short  series  of  foliums  mentioned  in 
§3  the  two  farthest  ventrad  constitute  'On.^t  flocculus.  To  isolate  it,  the 
tiers  farther  dorsad  must  be  torn  away  as  directed  in  §  3.  If  it  is  pushed 
caudad  it  will  be  seen  to  have  a  slender  stalk  of  its  own  connected  with 
the  caudal  margin  of  the  medipeduncle. 

a.  For  details  respecting  the  flocculus  and  the  cerebellum  see  Dr. 
B.  B.  Stroud's  paper  in  the /ottr.  of  Comp.  Neurology  for  June,  1895. 


64  Praetieum  X.    The   Paraeoelian  Floor. 

b.  Just  caudad  of  the  flocculus  and  peduncle  is  a  tufted  plexus  which  covers. (and  prob- 
ably closes)  a  lateral  extension  of  the  epicoele  The  relation  and  significance  of  these  parts 
are  still  under  investigation  ;  meantime  consult  Handbook  Fig.  4702  and  Vol.  IX,  p.  5i6.-~ 
If,  as  held  by  some,  these  lateral  recesses  open  into  a  subarachnoid  space,  the  general 
statement  in  Pract.  IX,  §  17,  must  be  qualified  accordingly. 

§8.  Opening  the  Left  Pai'acoele  (lateral  ventricle). — This  is  most 
safely  accomplished  in  its  cephalic  portion,  the  precoknu,  where  there  is 
but  one  mass  that  may  be  unintentionally  injured  by  cutting  too  deeply. 

a.  If  the  cerebrum  has  not  been  sliced  off  as  directed  in  Pract.  VIII, 
§§  13-16,  PI.  XVIII,  it  should  be  now. 

b.  Be/ore  7naking  any  of  the  incisions  here  directed  the  scalpel  should 
be  dipped  in  alcohol. 

c.  Note  the  location  of  the  cephalic  end,  genu,  of  the  CALLObUM, 
Plates  XVIII  and  XXIII,  and  bear  in  mind  (i)  that  the  cavity  to  be 
opened  is  nearly  at  its  level  ;  (2)  that  it  is  nearer  the  mesal  than  the  lat- 
eral margin  of  the  hemicerebrum  ;  (3)  that  the  near  proximity  of  the  cav- 
ity may  be  recognized  by  the  appearance  of  a  dark  area  2-3  mm.  in  diam- 
eter about  one-third  of  the  way  from  the  meson  to  the  lateral  border.  This 
dark  area  is  not  due  to  a  difference  in  the  color  of  the  mass,  but  only  to 
the  existence  of  the  cavity. 

d.  From  the  cephalic  slope  of  the  left  hemicerebrum  (PI.  XVIII  b) 
cut  a  triangular  slice,  the  thicker  end  including  a  part  of  the  surface  a, 
the  thinner  approaching  the  olfactory  bulb,  but  not  quite  reaching  it. 
If  this  does  not  open  the  cavity,  or  expose  the  dark  area  mentioned  in 
(<:),  remove  a  second  but  thinner  slice,  and,  others  if  necessary  till  the 
precornu  is  opened. 

e.  From  Fig.  3,  p.  69,  and  the  dotted  lines  in  PI.  XXIV,  note  that  the 
precornu  is  continuous  with  the  cavity  of  the  olfactory  bulb,  but  defer  the 
demonstration  for  the  present  ;  Pract.  XI,  §8. 

f  Remove  the  "corner"  between  the  surface  a  of  PI.  XVIII  and 
the  new  surface  b  so  as  to  expose  the  cavity  a  little  farther  caudad.  In- 
troduce tlie  tracer  cautiously  a  few  millimeters  only  and  note  that  there 
is  a  shallow  cavity  bounded  by  a  roof  and  floor. 

g.  Carefully  avoiding  cutting  the  floor,  remove  successive  thin  slices 
farther  and  farther  caudad  till  the  floor  of  the  exposed  cavity  presents  the 
appearance  shown  in  PI.  XXIV.  It  may  be  neces.sary  to  remove  a 
wedge-shaped  slice  from  the  caudal  end,  c,  and  to  use  the  scissors  care- 
fully at  the  mesal  side  of  the  cavity. 

h.  Since  the  cephalic  part  of  the  cavity  extends  not  only  laterad  but 
also  ventrad  there  is  a  natural  temptation  to  open  the  ventral  extension 
near  the  meson  ;  for  the  present  this  should  be  avoided. 

§  9.  The  Paraplexus. — In  the  middle  of  the  floor  of  the  paraccele  is 
a  vascular  fringe,  perhaps  lying  flat  as  in  PI.  XXIV,  perhaps  in  a  more 
compact  roll.  This  is  a  fold  of  pia,  with  blood-vessels,  all  covered  by 
endyma,  and  constituting  the  paraplexus.  How  it  gets  into  the  para- 
ccele is  discussed  in  the  lectures  ;  later  in  this  praetieum  (§  21)  its  relation 
to  the  velum  will  be  shown.  For  convenience,  at  this  stage,  on  the  left 
side  so  much  of  the  paraplexus  as  can  be  seen  should  be  trimmed  closely 
to  its  line  of  attachment,  but  not  pulled  upon. 

§  10.  The  Paraeoelian  Floor. — The  removal  of  the  paraplexus  ex- 
poses the  more  substantial  constituents  of  the  floor,  as  seen  in  PI.  XXIV. 
Cephalad  is  the  pear-shaped  caudatum,  the  convexity  of  which  really 
looks  quite  as  much  mesad  as  dorsad.  Farthest  caudad  is  the  hippocamp 
{hippocampus  major).  Between  it  and  the  paraplexus  is  a  less  distinct 
elevation,  the  fimbria. 


Practicum    X.    The  Medicor'nu.  65 

a.  The  Cella. — The  largest  portion  of  the  paraccele  corresponds  to  what  has  been 
called  the  CELLA  {cellamedia)  ;  see  Handbook  Figs.  4703,  4740,  4746,  Vol.  IX,  fig.  61,  and 
the  preparations  and  photographs.  In  man  there  are  three  extensions  of  the  cella  :  ceph- 
alic, PRECORNU,  ventral,  MKDICORNU,  and  candal,  POSTCORNU  ;  the  last  is  wanting 
in  the  sheep  as  in  most  other  mammals.     As  to  the  human  paratela,^  see  4  21,  y. 

S  II.  The  Medicornu. — At  tlie  caudal  end  of  the  paraccele  there  is 
evidently  the  beginning  of  a  ventral  extension,  the  medicornu.  Intro- 
duce the  tracer  for  a  few  mm.,  on  the  left  side,  and  remove  a  slice  of  the 
caudal  end  of  the  hemicerebrum  ;  by  constantly  "feeling  one's  way" 
and  removing  thin,  wedge-shaped  slices,  it  will  be  po.'^sible  to  follow  this 
horn-shaped  extension  of  the  paraccele  ventrad,  laterad,  cephalad,  and  at 
last  even  slightly  mesad  to  the  extremity  of  the  elevation  on  the  ventral 
aspect  of  the  brain  which  overlaps  the  optic  tract  and  is  numbered  ./  in 
PI.  XIX. 

a.  The  complete  exposure  of  the  medicornu  will  involve  cutting 
away  a  considerable  part  of  the  caudal  and  lateral  portions  of  the  hemi- 
cerebrnm,  as  indicated  in  PI.  XXIV.  The  convexity  of  the  tracer  mav 
be  used  in  pushing  up  the  overhanging  edges  of  the  parietes  so  that  they 
may  be  more  easily  cut  away  with  tlie  scalpel  or  in  some  cases  the  scis- 
sors. Toward  the  ventral  end,  the  tip  of  tlie  medicornu,  especial  care 
must  be  taken  not  to  pull  or  push  upon  the  parts  lest  they  break  at  some 
of  the  thinner  places. 

b  It  will  be  found  that  the  iiippocamp  is  not  regularly  convex  as  in- 
dicated by  PI.  XXIV,  but  flattened  slightly  in  places,  and  terminates  as 
a  blunt  point  at  the  tip  of  the  cornu. 

c.  Tlie  fimbria  maintains  a  nearly  uniform  width  and  surface. 

d.  The  paraplexus  continues  to  near  the  tip,  and  should  be  trimmed 
closely,  as  directed  in  §9,  but  ivithoiit  pulling  ttpoji  it. 

e.  The  caudatum,  as  already  seen  (§  10),  tapers  caudad  ;  there  seems 
to  be  some  difference  among  the  brains  as  to  the  extent  of  its  cauda 
along  the  medicornu.  In  the  sheep  the  writer  has  not  as  yet  recognized 
the  tenia  of  the  human  brain  ;  HavdbookVW\  145. 

f.  Note  that  in  potassium  dichromate  specimens,  the  fimbria  and 
hippocamp  are  light  (alba)  while  the  caudatum  is  dark  (cinerea). 

§  12.  Make  a  drawing  of  the  dissection  at  this  stage  from  the  lateral 
and  ventral  aspects.  In  combination  with  PI.  XXIV  they  will  illustrate 
the  notable  changes  in  the  direction  or  the  cavity  ;  it  extends  success- 
ively caudad,  laterad,  ventrad,  cephalad  and  mesad. 

§  13.  Tra7isecting  the  Right  Medicornu. — In  accomplishing  this 
there  is  to  be  removed  a  mass  representing  approximately  the  ventro- 
latero-caudal  eighth  of  the  right  cerebrum  ;  on  PI.  XIX  the  piece  is 
bounded  as  follows  :  Laterad  and  caudad  by  the  general  outline  ;  mesad  by 
the  S-shaped  mesal  border  of  the  olfactory  tract,  along  the  numbers  j,  / 
and  (5/ cephalad  by  an  imaginary  line  drawn  latero-dorsad  from  the  chiasma. 
The  two  incisions  required  to  dislodge  this  piece  are  to  be  made  as  fol- 
lows : 

a.  Hold  the  brain  with  the  myel  away  from  you  and  the  ventrum 
uppermost.  With  the  scalpel  point,  from  the  depressed  area  just  laterad 
of  the  cliasma  (PI.  XIX,  j),  cut  laterad  and  very  slightly  cephalad  across 
the  olfactory  tract  and  into  the  pallium  for  about  the  same  distance,  stop- 
ping at  the  greatest  lateral  convexity  of  the  cerebrum. 

b.  Turn  the  brain  so  that  the  right  side  is  uppermost.  Dip  the  scal- 
pel in  alcohol.  Begin  at  the  caudal  margin  of  the  cerebrum  opposite  the 
flocculus.  Push  the  point  in  for  at  least  2  cm.  (nearly  an  inch)  and  cut 
with  a  sawing  movement  to  the  lateral  end  of  the  first  incision. 


66  Practicum  X.    The   Hippoeamp  and  Fimbria. 

c.  If  the  caudal  end  of  the   part  ventrad  of  the  incision  be  gently 
elevated  it  may  be  detached  ;  the  operation  should  be  performed  slowly 
and  the  scissors  used  promptly  for  dividing  any  vessels  that  ma}-  resist  the' 
separation  ;  all  pulling  should  be  avoided. 

d.  The  detached  piece  is  to  be  wet  with  alcohol,  and  handled  with 
great  care,  for  reasons  that  will  appear  presently. 

§  14.  From  the  undulating  surface  exposed  by  its  removal  remove 
the  tough  and  adherent  pia,  beginning  at  the  margin  of  the  pons,  and 
note  that  at  the  cephalic  margin  of  the  optic  tract  it  ceases  by  an  irreg- 
ular edge,  evidently  torn.  Compare  the  denuded  parts  with  PI.  XX I 
where,  however,  everything  is  reversed,  since  it  represents  the  left  side.- 

§  15.  Examine  the  concave  mesal  surface  of  the  detached  piece, 
handling  it  as  little  as  possible  and  note  that  its  natural  surfaces  are  also 
covered  by  pia  ;  defer  the  removal  of  the  pia  till  the  cut  surface  has  been 
examined. 

§  16.  On  either  cut  surface  (more  conveniently  on  that  of  the  de- 
tached piece)  the  following  features  may  be  observed  and  a  drawing  made 
if  time  permits. 

a.  Not  far  from  the  middle  of  the  length,  but  nearer  the  mesal  than 
the  lateral  surface,  a  crescentic  slit,  its  convexity  directed  laterad  ;  from 
comparison  with  the  leftside  this  can  be  nothing  else  than  the  transected 

MEDICORNU. 

b.  The  lateral  wall  of  the  cavity  is  consituted  by  the  general  mass 
of  the  ALBA,  but  the  convex  mass  at  its  mesal  side  is  mostly  cinerea,  with 
a  cephalic  edge  of  alba.  Comparison  with  the  floor  of  the  left  medicornu 
.shows  that  these  are  respectively  the  hippocamp  and  the  fimbria. 

c.  The  cortex  at  the  lateral  side  of  the  section  may  be  traced  caudad 
over  the  end  of  the  hemicerebrnm  to  the  mesal  side,  with  the  usual  undu- 
lations at  the  fissures.  For  a  short  distance  on  the  mesal  side  near  the 
caudal  end  it  is  thin,  but  thickens  suddenly  at  the  hippocamp. 

d.  Opposite  the  cephalic  portion  of  the  cut  end  of  the  hippocamp 
is  a  slit  which  may  be  traced  to  the  ventral  end  of  the  piece  ;  this  is  the 
HIPPOCAMPAL  FISSURE,  probably  the  most  constant  of  all  the  mammalian 
fissures  and  one  of  the  earliest  to  appear  in  development. 

e.  The  alba  forming  the  central  part  of  the  general  section  is  thin 
in  the  caudal  part  of  the  roof  of  the  cornu,  thickens  somewhat  just  cau- 
dad of  the  cornu,  on  the  ental  surface  of  the  hippocamp  becomes  so  thin 
as  to  be  hardly  recognizable,  but  constitutes  the  whole  of  the  fimbria. 

§  17  It  appears  then  that  the  hippocamp  and  fimbria  are  simply 
specialized  parts  of  the  paraccelian  parietes,  but  with  inverse  proportions 
of  the  two  constituents  ;  the  former  consists  mostly  of  cinerea,  being  thus 
properly  a  cortical  part ;  the  latter  consists  wholly  of  alba,  being  thus  a 
medullary  part  ;  Pract.  VIII,  §  13. 

§  18.  77/1?  Rima. — As  has  doubtless  been  observed  already,  along  the 
cephalic  margin  of  the  fimbria  is  a  crevice  between  it  and  the  surface 
that  broke  away  when  the  piece  was  detached.  This  is  the  rima  (part  of 
the  "great  transverse  fissure"). 

§  19  Under  favorable  conditions,  if  the  piece  is  manipulated  so  as  to 
put  the  mesal  surface  slightly  on  the  stretch,  the  following  points  may  be 
observed  : 

a.  The  rima  will  be  widened  especially  near  the  cut  end. 

b.  At  the  other  (ventral)  end  it  ceases  a  few  mm.  from  the  extremity, 
although  a  rupture  easily  occurs  so  as  to  extend  the  natural  crevige. 


Practicuni    X.     The  Rima.  67 

c.  At  one  or  more  points  in  its  course  there  are  membranous  adhe- 
sions of  the  margins  of  tlie  rima. 

d.  These  adhesions  are  more  apt  to  persist  in  brains  hardened  with 
alcohol,  especially  if  the  cavities  have  been  filled  with  the  preservative. 

e.  Within  the  medicornu  is  a  membranous,  vascular  lamina,  the 
PARAPLEXUS,  already  seen  on  the  left  side  (§  9).  It  commonly  rests  closely 
against  one  of  the  walls,  but  may  be  separated  therefrom  with  tiie 
tracer  or  a  stream  of  air.  One  edge  is  free  ;  the  other  readies  the  rima 
and  is  there  connected  with  its  margins. 

§  20.  If  now  the  pia  be  removed  from  the  mesal  surface  of  the  piece, 
beginning  at  the  caudal  margin,  it  will  be  found  to  dip  into  the  hippo- 
campal  fissure  as  a  fold,  and  then  to  continue  over  the  fimbria  to  the  rima 
where  it  connected  with  the  paraplexus.  At  the  rima  or  just  cephalad  of 
it,  however,  it  was  torn  when  it  was  removed  ;  otherwise  it  would  be 
found  to  be  reflected  caudad  upon  the  optic  tract,  etc. 

a.  The  piece  may  now  be  bent  so  as  to  open  the  rima  widely  and 
expose  the  cornu  and  plexus.  The  latter  will  be  found  to  cease  at  about 
5  mm.  from  the  extremity  of  the  piece.  A  careful  examination,  espec- 
ially of  an  alcoholic  preparation,  would  show  that  the  rima  also  ceases 
there,  and  that  its  apparent  extension  is  also  due  to  the  rupture  of  the 
thin  wall. 

§  21.  The  relation  of  these  parts  and  their  interpretation  from  embry- 
ology and  comparative  anatomy  are  considered  more  fully  in  Analoniical 
Technology,  §  13 12,  and  in  the  Handbook  VII  pp.  1 18  and  144.  Here  it  can 
only  be  stated  tliat,  notwithstanding  the  ease  with  which  the  margins  of 
the  rima  may  be  separated  in  preserved  specimens,  the  dissection  ot  fresh 
brain  and  tlie  study  of  sections  of  liardened  ones  leave  no  doubt  respect- 
ing the  following  points  : 

a.  Between  the  overlapping  parts  of  the  cerebrum  and  the  genicu- 
lums,  etc.,  are  two  layers  of  pia,  one  belonging  to  the  diencephal,  the 
other  to  the  prosencephal. 

b.  These  two,  with  the  vessels  between  them,  constitute  the  velum. 

c.  Were  there  no  rima,  the  continuity  of  the  two  apposed  layers  of 
the  velum  would  be  along  the  cephalic  margin  of  the  optic  tract,  at  the 
boundary  between  the  two  segments. 

d.  The  interruption  of  the  continuity  of  the  wall  of  the  paracoele, 
from  the  dorsal  end  of  the  porta  to  near  the  tip  of  the  medicornu,  consti- 
tuting the  rima,  permits  the  entrance  of  the  margin  of  the  velum  into 
the  paraccele  as  a  paraplexus. 

e.  The  paraplexus  carries  before  it  the  lining  endynia,  which  there- 
fore, although  extended  over  the  plexris,  connects  the  two  margins  of  the 
rima,  and  thus  maintains  endymal  continuity  and  coelian  circumscription  ; 
Pract.  IX,  §  17. 

f.  In  the  human  adult  the  rima  is  i — 2  cm.  wide  at  the  middle  of 
its  length,  tapering  at  the  ends.  The  interval  is  closed,  however,  by  the 
apposed  endyma  and  pia,  constituting  the  paratela.  Through  this  thin* 
translucent  strip  appears  the  subjacent  thalamus,  to  which  it  sometimes 
adheres  ;  this  has  given  rise  to  the  statement  current  in  works  on  Descrip- 
tive Anatomy  that  the  thalamus  enters  into  the  composition  of  the  floor  of 
the  "lateral  ventricle."  A  similar  condition  exists  in  apes.  But  in  the 
human  fetus,  up  to  four  months  at  least,  the  rima  is  narrow  as  in  the 
sheep  and  most  other  mammals.  See  the  figures  referred  to  in  §  10  a,  also 
Fig.  4749,  and  the  writer's  paper,  "The  relation  of  the  thalamus  to  the 
paraccele,"  Jour,  of  Nerv.  and  Mental  Disease,  '^\\\\\  1889. 


PRACTICUM  XI:  DISSECTION  OF  THE  SHEEP'S  BRAIN  CONTINUED";, 
STUDY  OF   TRANSECTIONS. 


§  I.  Exposing  the  Right  Paracoele. — This  may  be  done  (see  Pr.  X, 
§8)  with  some  confidence  at  the  cephalic  and  caudal  ends,  using  the 
left  as  a  guide,  since  presumably  the  parts  are  at  the  same  level  on  the 
two  sides. 

§  2.  Removing  the  Callosiim. — Between  the  two  paracoeles  and 
slightly  overhanging  their  mesal  parts  is  the  mesal  portion  of  the  callos- 
um.  The  overhanging  thin  portions  are  to  be  trimmed  off  carefully  with 
scissors, 

§  3.  The  Septum. — But  when  the  intermediate  portion  of  the  callosum 
is  removed  it  will  be  found  that  the  two  paracoeles  are  separated  at  the 
meson  by  a  thin  partition  which  is  very  easily  torn.  This  is  the  SEPTUM 
{septum  liicidiim  of  Human  Anatomy). 

§4.  The  Pseudoccele. — By  reference  to  Plates  XXII,  XXIII  and 
XXIV  and  to  Pract.  IX,  §  19  it  will  be  seen  that  this  partition  be- 
tween the  two  paracoeles  is  really  double  ;  each  half,  hemiseptum,  repre- 
sents part  of  the  mesal  wall  of  the  corresponding  paracoele.  Their  dor- 
sal portions  are  often  so  thin  and  so  closely  apposed  as  to  be  separated 
with  difficulty  ;  in  PI.  XXIV  they  and  the  intervening  slit-like  pseudo- 
code are  too  thick. 

§5.  The  Genu  and  Spleniiim. — At  the  cephalic  end  the  callosum 
turns  ventrad,  as  seen  in  PL  XXIII  ;  it  also  extends  laterad  and  cephalad, 
the  right  and  left  halves  diverging  at  about  a  right  angle.  The  conditions 
are  nearly  the  same  at  the  caudal  end,  the  splenium. 

§  6.  On  the  left  side,  from  the  region  between  the  cephalic  slope  and 
the  medicornu  (corresponding  nearly  on  PI.  XXIV  with  the  unshaded 
area  between  lines  5  and  g)  remove  a  slice  2-3  mm.  thick.     Note  : 

a.  The  undulations  of  the  cortex,  corresponding  with  the  insula 
(island  of  Riel)  of  the  human  brain,  less  covered  in  the  sheep. 

b.  The  gray  mass  of  caudatum,  constituting  thus  an  entocinerea. 

c.  The  intermediate  alba  into  which  more  or  less  of  the  entocinerea 
intrudes  in  streaks,  giving  the  appearance  which  has  caused  the  name 
STRIATUM  to  be  applied  to  this  tliickened  portion  of  the  parietes. 

d.  If  time  permits  make  a  drawing  of  this  section. 

§7.  Demonstration  of  the  Porta. — Remove  part  of  the  caudatum  as 
follows  :  On  PI.  XXIV  draw  two  pencil  lines  from  a  point  corresponding 
with  the  bottom  of  the  fissure  8  respectively  to  the  mesal  end  of  lines  5 
and  9.  Cut  along  the  two  lines  holding  the  scalpel  so  that  it  is  at  about 
45°  with  the  cut  dorsal  surface.  On  pushing  out  the  piece  thus  separated 
and  trimming  off  the  free  cephalic  end  of  the  paraplexus  there  will  be 
found  an  orifice  2-3  mm.  long  and  about  i  mm.  wide,  oblique  in  direction 
and  admitting  the  tracer  or  probe  meso-ventro-caudad.  This  is  the  porta 
(foramen  of  Monro)  of  the  left  side,  the  sole  communication  between  the 
left  paracoele  and  the  aula,  the  mesal  division  of  the  prosccoele,  and  thus 
indirectly  the  other  mesal  cavities  ;  see  Handbook  Figs.  4710,  4729,  4739- 
4745,  and  Pract.  IX,  §  14^'. 


Praeticum    XI.     The  Rhinoeoele.  69 

§8.  Demonsiratiiig  the  Continiiily  of  the  Paraccele  with  the  Rhino- 
eoele.— This  continuity  is  shown  from  the  dorsal  side  in  Fig.  3  and  from 
the  ventral  in  preparation  No.  2653.  It  may  be  exposed  from  the  left 
side  as  follows  : 

a.  From  the  left  side  cut  oflF  successive  slices,  being  guided  by  the 
dotted  line  /  in  PL  XXIV  and  by  the  line  of  the  paracoele.  The  result- 
ant surface  will  be  concave,  and  look  laterad  and  also  slightly  dorsad.  If 
the  cuts  are  made  cautiously  the  precornu  may  be  traced  tlirough  the 
olfactory  crus  as  a  very  narrow  passage,  expanding  considerably  in  the 
bulb.  Compare  Handbook  Fig.  4729  and  Ajiatomical  Technology.,  PL  IV, 
Fig.  16.     Tliis  stage  should  be  drawn  from  the  left  side  if  time  permits. 


olf.  strait 
medulla  (alba) 
cortex  (cinera) 
precornu 


Fig.  3. 
EXPOSED 


LEFT    OLFACTORY     BULB     OF    THE     SHEEP, 
X  2.     From  a  preparation  by  Dr.  P.  A.  Fish. 


THE    RHINOCCELE 


The  object  is  to  show  the  continuity  of  the  paracoele  with  the  cavity  of  the  olfactory 
bulb  through  the  narrow  strait.  Compare  Plates  XVIII  and  XXI L  See  Pract.  IX,  |  6, 
for  fuller  consideration  of  the  relations  of  these  cavities. 


§9.  The  Precomniissure.—Ow  PL  XXIII  note  the  location  of  the 
mesal  section  of  the  commissure  just  ventrad  of  the  porta.  Draw  an  im- 
aginary line  on  that  figure,  or  on  a  real  meson,  beginning  at  the  depres- 
sion (postcribrum)  just  caudad  of  the  albicans,  passing  between  the  chi- 
asma  and  the  precominissure,  then  ventrad  to  the  genu  and  so  to  the 
cephalic  convexity  of  tlie  cerebrum. 

a.  From  the  specimen  cut  away  so  much  as  may  be  estimated  to  lie 
ventrad  of  this  line,  being  guided  by  the  location  of  the  porta,  the  level 
of  which  should  not  be  reached  by  the  first  incision  by  at  least  2  mm. 

b.  On  the  right  may  be  recognized  the  alternate  streaks  of  alba  and 
cinerea  constituting  the  striatum  which  has  been  divided  on  the  left  by  a 
sagittal  section  (§  6,  c). 

c.  From  the  region  just  ventrad  of  the  porta  very  cautiously  remove 
thin  slices,  until,  just  cephalad  of  the  mesal  cavity  (cephalic  part  of  dia- 
coele),  there  appears  a  well  defined  tract  of  alba  about  i  mm.  in  diameter, 
crossing  the  meson  and  curving  cephalad  so  as  to  form  a  crescent.  This 
is  the  PRECOMMissuRE  (anterior  commissure).  The  cephalic  arms  might 
be  traced  to  the  olfactory  bulbs,  of  which  they  constitute  a  commissure, 
as  seen  in  preparation  No.  2653  ;  a  pair  of  caudal  arms  is  less  easily 
traced  into  the  corresponding  hemicerebrums. 

§10.  The  Aula  and  Portas. — Dip  both  the  specimen  and  the  scal- 
pel in  alcohol  ;  note  the  location  of  the  porta  as  exposed  on  the  left  side  ; 
apply  the  edgealongthe  oblique  sinistro-cephalic  margin  of  the  cerebrum 


70  Practieum  XI.     The   Aula. 

a.s  left  by  the  previous  dissection,  and  at  one  sweep  remove  so  much  as 
lies  ventrad  of  the  middle  of  the  porta. 

a.  If  both  portas  have  been  thus  transected  they  will  be  found  tp  be 
narrow  passages  converging  caudo-mesad  to  a  small  mesal  cavity,  the 
AULA. 

§  II.  The  cut  area  cephalad  of  the  transverse  passage  thus  consti- 
tuted is  nearly  square,  its  four  sides  forming  angles  of  about  45°  with  the 
meson,  but  the  two  cephalic  sides  are  prolonged  as  the  nearly  parallel 
borders  of  a  thin  mesal  extension,  tlie  septum  between  the  two  paracoeles, 
commonly  called  septum  huiduvi. 

a.  If  the  tracer  (better  the  syringotome)  be  applied  accurately  at  the 
middle  of  the  total  area  and  gently  pushed  cephalad  upon  the  meson,  the 
tip  of  the  left  index  being  at  the  time  applied  just  dorsad  of  the  cut  end 
of  the  mass,  it  will  be  found  tiiat  the  apparently  continuous  surface  may, 
in  its  cephalic  portion,  be  separated  at  the  meson  into  a  right  and  left 
portion,  each  tapering  into  the  corresponding  half  of  the  thin  projection 
just  mentioned. 

b.  Each  of  these  thin  lateral  parts  is  a  hemiseptum  ;  the  mesal 
space  between  them  is  the  pseudoccELE  ("fifth  ventricle")  PI.  XXIII, 
Pract.  IX,  §  19,  b,  and  Plates  XXIV  and  XXV. 

The  thicker  lateral  portions  are  the  fornicolumns  (pillars  of  the 
fornix)  united  at  the  meson  ;  see  §  31. 

c.  The  masses  just  caudad  of  the  portas  are  the  thalami,  joined 
across  the  meson  by  the  large  medicommissure,  which,  unlike  the  pre- 
commissure,  consists  of  cinerea.  The  cut  surfaces  exposed  present,  be- 
sides some  smaller  tracts,  extensive  areas  of  alba  diverging  from  the  pons 
cephalad  in  the  crura,  and  laterad  of  the  thalami  as  the  "internal  cap- 
sule" and  radiating  in  the  substance  of  the  cerebrum. 

§  12.  Remove  the  remnant  of  the  right  striatum  along  the  cephalic 
margin  of  the  fimbria,  and  transect  the  left  hippocamp,  etc.^  at  the  same 
level  as  the  right  ;  the  brain  is  now  nearly  symmetric. 

§  13.  Trim  off  so  much  of  the  caudal  end  of  each  hemicerebrum  as 
lies  caudad  of  the  medicornu,  that  is,  so  much  as  in  PI.  XXIV  projects 
beyond  the  furrow  marked  10  ;  this  will  include  also  the  splenium,  the 
caudal  end  of  the  callosum.  While  cutting,  a  finger  should  be  kept  upon 
the  middle  of  the  mass  to  steady  it. 

a.  There  will  now  be  exposed  the  large  pregeminum,  already  seen 
in  PL  XXII,  and  at  the  meson,  upon  its  cephalic  margin,  a  soft,  ragged 
mass.  This  might  well  be  mistaken  for  the  conarium,  but  it  is  really  the 
membranous  sack  upon  the  conarium  itself,  indicated  inadequately  in  PI. 
XXIII,  and  mentioned  in  Pract.  IX,  §  12,  e.  The  tip  of  the  sack  has  per- 
haps been  opened  in  cutting  off  the  splenium  ;  it  should  be  cut  off  cleanly 
with  the  scissors  to  expose  its  considerable  cavity  and  the  plexuses  that 
cover  its  ental  surface.  The  examination  of  the  conarium  itself  may  be 
deferred  for  the  present. 

§14.  The  Fornix. — The  curved,  cap-like  mass  now  visible  cephalad 
of  the  pregeminum  and  conarium  is  composed  of  the  following  parts  : 
The  two  fimbrias  at  the  margins  ;  the  two  hippocamps  nearer  the  meson  ; 
at  the  meson,  the  remnant  of  the  septum  ;  and,  concealed  thereby,  the 
conjunction  of  the  two  pairs  of  parts.    Now  although  the  hippocamp  and 


Praetieum   XI.      The     Fornix.  71 

fimbria  of  either  side  are  primarily  mere  constituents  of  the  floor  of  the 
paracoele  of  that  side,  yet  since  the  fimbria  is,  in  one  sense,  disconnected 
from  the  parietes  at  the  opposite  side  of  therima,  and  since  the  hippo- 
camps  are  united  at  the  meson,  therefore  it  is  often  convenient  to  deal 
with  this  secondary  combination  of  parts  under  the  single  name,  fornix  ; 
see  Handbook,  VllI,  pp.  13S-139. 

§  15.  Removal  of  the  Fornix. — In  the  preparation  from  which  PI.  XXII 
was  drawn,  the  fornix  was  pushed  off  hastily,  carrying  with  it  the  mem- 
branous roof  of  the  diaccEle.     This  may  be  avoided  as  follows  : 

a.  At  either  side  lift  the  cut  end  of  the  fimbria  and  hippocamp 
enough  to  disclose  vessels  and  bands  passing  between  them  and  the  sub- 
jacent parts  ;  divide  these  with  the  scissors  and  repeat  on  the  other  side 
till  the  meson  is  approached  ;  here  special  pains  must  be  taken,  and  it 
may  be  necessary  with  the  forceps  to  pull  the  conarial  sack  from  the 
recess  between  the  mesal  ends  of  the  gyres  bordering  the  hippocamp 
fissure. 

b.  When  the  lateral  and  caudal  parts  of  the  fornix  are  free  the  whole 
may  be  gently  pushed  dorsad  and  diconnected  ;  dip  it  in  alcohol. 

§  16.  The  Conarial  Sack. — Push  this  away  from  the  conarium  a  little 
and  place  the  tip  of  the  thumb  on  the  apex  of  th-e  conarium  so  as  to 
steady  it  ;  the  sack  may  then  be  pushed  and  pulled  from  the  dorsal 
(properly  cephalic)  aspect  of  the  conarium. 

§  17.  The  Velum. — The  pia  covering  the  diencephal  and  mesence- 
phal  and  the  apposed  ventral  surface  of  the  fornix  constitutes  the  velum. 
Its  latero-cephalic  borders  are  the  paraplexuses  ;  one  of  these  has  been 
trimmed  off"  but  the  dorsal  part  of  the  right  should  remain  ;  Pract.  X, 
§21. 

§18.  The  Velar  Vein. — This  was  mentioned  in  Pract.  IX,  §25,  a. 
It  may  now  be  seen  just  cephalad  of  the  conarium,  formed  by  the  junc- 
tion of  a  pair  from  opposite  sides.  The  corresponding  velar  arteries  are 
not  easy  to  recognize  unless  the  arteries  have  been  injected. 

§  19.  The  Diaiela. — At  the  meson  and  for  2-3  mm.  at  either  side  the 
velum  covers  the  diacoele  ;  it  is  here  more  vascular,-  and  thicker  from  the 
fusion  with  it  of  the  endyma,  and  from  the  formation  of  the  diaplexu.ses  ; 
this  mesal  strip  is  the  diatela,  seen  in  transection  in  PI.  XXV. 

§  20.  The  cephalic  end  of  the  diatela  presents  a  deep  notch,  corre- 
sponding to  a  triangular  area  (the  delta)  on  the  ventral  surface  of  the 
fornix  which  here  constitutes  the  roof  of  the  aula  ;  see  Anatomical  Tech- 
nology, §  12 17,  and   PI.  IV,  Fig.   14. 

§  21.  The  Habena. — Introduce  at  the  notch  just  indicated  the  point 
of  the  narrower  blade  of  the  scissors  and  medisect  the  diatela  to  the  hole 
made  by  cutting  off  the  sack  (§30).  Reflect  the  halves  in  opposite  direc- 
tion. At  the  sides  of  the  diacoele  will  be  seen  the  habenas  already 
studied  from  the  mesal  aspect  in  Pract.  IX,  §  16.  If  the  dissection  has 
been  done  carefully,  just  laterad  of  the  habena  will  be  recognized  the  line 
of  reflection  of  the  endyma  upon  the  diatela  constituting  the  lateral 
boundary  of  the  diacoele.  If  upon  either  side  the  diatela  and  velum  be 
torn  off",  along  that  line  will  be  left  a  membranous  ridge,  the  ripa,  the 
.ragged  edge  of  the  combined  pia  and  endym.     This  ripa  may  be  traced 


72  Practicum  XI.    The  Study   of  Transections. 

to  the  dorsal  end  of  the  porta,  and  thence  latero-caudad  along  the  rima. 

§22.  The  Medicommissure. — This  has  been  cnt  from  the  ventral 
aspect  in  §  ii,  c,  and  is  shown  in  Plates  XXIII  and  XXV.  Its  presence, 
size  and  circular  outline  ma^^  be  recognized  now  by  divaricating  the 
thalami  slightly  and  letting  the  light  strike  between  them.  In  the  sheep 
as  in  most  mammals  it  is  much  larger  than  in  man. 

§  23.  The  Study  of  Transections. — To  each  four  members  of  the 
section  will  be  supplied  a  set  of  transections  of  one  brain,  to  be  handled 
with  great  care.  But  if  preferred,  as  suggested  in  Pract.  X,  §  2,  «,  certain 
of  their   own    specimens  may  be   transected,  and    then  examined    more 

freely. 

§  24.  The  following  general  propositions,  suggestions,  and  directions 
as  to  the  study  of  transections  of  the  brain  apply  for  the  most  part  to 
other  organs,  to  entire  animals  and  in  some  respects  to  microscopic  sec- 
tions as  well. 

§25.  The  two  cut  surfaces  resulting  from  a  transection  at  a  given 
level  are  identical  in  form  and  composition. 

a.  After  the  section  is  made  one  or  both  of  the  surfaces  may  be 
trimmed  or  sliced  off,  or  imprinted  or  otherwise  modified  from  its  origi- 
nal condition,  but  this  does  not  affect  the  correctness  of  the  general 
proposition. 

§26.  Wiien  a  transected  region  contains  a  cavity  both  cut  surfaces 
will  present  interruptions  of  equal  area  and  form. 

§  27.  If  the  transected  cavity  continues  of  uniform  shape,  size  and 
direction  in  both  directions  then  photographs  or  shaded  drawings  of  the 
two  surfaces  will  be  identical  in  that  respect  also. 

a.  But  if  the  cavitv  changes  in  size,  shape  or  direction,  then  cor- 
responding differences  will  appear  in  the  photograph  or  in  an  accurate 
shaded  drawing. 

§28.  Absolute  transections  of  a  perfectly  symmetric  mass,  e.g..,  a 
regular,  homogeneous  cylinder,  will  produce  symmetric  cut  surfaces  ;  i.  e.., 
the  right  and  left  will  be  identical  in  form  and  composition  although 
reversed  in  direction. 

a.  But,  firstly,  even  were  the  two  halves  of  a  brain  absolutely  ident- 
ical, originally,  some  asymmetry  always  results  from  the  manipulations 
and  agencies  to  which  it  is  subjected. 

b.  Secondly,  it  is  probable  that  no  absolutely  exact  transection  of  a 
large  and  complex  brain  like  that  of  the  sheep  is  ever  made. 

§  29.  The  student  must  be  prepared  for  recognizable  and  sometimes 
marked  differences  between  the  right  and  left  sides  of  the  section. 

a.  An  absolutely  symmetric  drawing  of  a  transection  justifies  the 
inference  that  one  side  has  been  simply  copied  from  the  other. 

§30.  In  drawing  transections  of  the  brain,  and  indeed  of  most  or- 
gans or  organisms,  there  commonly  arises  a  practical  difficulty  due  to  the 
great  difference  in  the  size  of  parts.  A  drawing  of  moderate  size  may  leave 
the  smaller  features  obscure,  while  an  enlargement  of  the  whole  such  as 
to  exhibit  these  features  clearly  may  waste  space  and  time. 

§  31.     The  difficulty  may  be  met  in  either  of  three  ways  : 


Practicum  XI.    The  Study   of  Transections.  73 

1.  The  whole  may  be  shown  of  moderate  size  and  the  more  complex 
areas  enlarged  sufficiently  as  separate  drawings.  This  is  the  common 
method  with  maps  and  is  employed  on  PL  XXV. 

2.  The  whole  may  be  enlarged,  but  time  may  be  saved  by  not  in- 
cluding certain  features  where  the  omission  would  occasion  no  misappre- 
hension. For  example,  on  PI.  XXIII  the  subdivisions  of  the  cerebellum 
are  omitted,  the  omission  being  stated  in  the  description.  On  PI.  XXV 
a  part  or  all  of  the  ciuerea  might  have  been  indicated  merely  by  a  line 
corresponding  with  its  ental  inargin. 

3.  With  transections,  unless  it  be  desired  to  exhibit  differences  be- 
tween the  two  sides,  natural  or  caused  by  the  obliquity  of  the  section,  a 
portion  of  one  side  may  be  omitted  altogether,  as  in  Fig.  122  of  Anatom- 
ical Technology. 

Whichever  method  is  adopted  it  is  well  to  remember  that  drawings 
are  seldom  on  too  large  a  scale. 

§  32.  While  it  is  desirable  to  maintain  the  natural  proportions  of  the 
several  parts  and  cavities,  the  cavities  may  be  somewhat  reduced,  if  neces- 
sary, in  order  to  afford  space  for  the  distinct  representation  of  outlines. 

a.  For  instance,  the  cavities  of  the  diacoele  and  the  paracoele  may 
be  encroached  upon  for  the  sake  of  indicating  distinctly  the  membranes 
and  plexuses. 

b.  On  the  other  hand,  where  the  parts  are  superposed,  as  the  cere- 
bellum upon  the  geminum  and  the  cerebrum  on  the  cerebellum,  it  is  per- 
missible to  increase  the  distance  between  them  so  as  to  represent  the  out- 
lines, meninges,  etc. 

§  33.  Keeping  in  mind  what  was  said  in  §  26,  an  admirable  test  of  the 
student's  powers  of  observation,  interpretation  and  delineation  will  be 
afforded  by  his  drawing  the  two  cut  surfaces  made  by  a  given  transection 
at  two  different  times  and  then  comparing  ;  still  more  severe  will  be  the 
test  if  these  surfaces,  or  one  of  them,  be  so  drawn  by  two  individuals. 

§  34.  The  general  level  of  a  transection  may  be  determined  by  unit- 
ing the  section  with  its  neighbors. 

§  35.  The  exact  level  may  require  the  detailed  comparison  of  the 
principal  or  most  easily  identified  features  (cavities  or  masses)  with  the 
meson  (PI.  XXIII)  and  with  the  dissections  (Plates  XX-XXIV). 

§  36.  It  will  be  easier  for  the  beginner  to  take  first  the  mesencephalic 
transection  (D)  both  because  a  single  segment  only  is  included  and  be- 
cause the  cavities  and  walls  are  comparatively  simple.  Next  sections  G 
and  F,  then  C  and  B,  and  lastly  E  (PI.  XXV). 

§37.     Section  C  presents  special  difficulties  of  two  kinds. 

a.  The  cerebellar  outline  is  very  irregular  on  account  of  the  numer- 
ous foliums  and  the  intervening  rimulas.  These  need  be  represented  on 
one  side  only. 

b. — The  cavity  is  a  horse-shoe-shaped  slit,  concave  dorsad,  and  nearlv 
filled  by  a  projecting  mesal  lobe  of  the  cerebellum.  But  really  between 
this  lobe  and  the  oblongata  there  is  a  delicate  lamina,  the  lingula  (PI. 
XXIII).  The  space  ventrad  of  the  lingula  is  the  epicoele,  a  part  of  the 
true  brain  cavity  ;  the  space  dorsad  is  seen  in  PI.  XXIII. 

§38.     With  section  B  the  conditions  are  similar.      Between  the  post- 


74  Praelicum  XI.     Defibrillation. 

oblongata  and  the  overhanging  cerebellum  intervenes  the  membranotis 
metatela,  the  roof  of  the  nietaccEle,  and  this  may  adhere  so  closely  to  the 
cerebellum  as  to  be  at  first  ignored. 

§  39.  With  section  F  the  main  difficulty  is  due  to  the  thinness  of  the 
dorsal  part  of  the  septum  and  the  narrowness  of  the  pseudocoele  betweeij 
the  two  halves. 

§40.  Defibrillatio7t. — The  fibrous  structure  of  certain  regions  may 
be  roughly  demonstrated  upon  a  half-brain  as  follows  : 

a.  Grasp  the  chiasma  and  pull  latero-dorso-caudad.  The  optic 
TKACT  may  be  separated  from  the  subjacent  parts  and  traced,  gradually 
widening,  over  the  lateral  aspect  of  thepregeniculum  and  perhaps  to  the 
pregeminum. 

b.  Grasp  the  cerebelltim  and  pull  laterad  and  then  ventrad  ;  the 
MEDIPEDUNCLE  will  be  seen  to  be  cnntinuous  with  the  pons. 

c.  Grasp  the  olfactory  htilb  and  pull  ventro-caudad   so  as  to  tear  off 

the  OLFACTORY    TRACT. 

d.  Divide  the  posioblongaia  by  a  sagittal  section.  Pull  the  lateral 
and  mesal  portions  apart  slowly  and  steadil}'.  The  separation  will  con- 
tinue into  the  cerebrum  and  the  fibrous  structure  will  be  particularly 
obvious  in  theCRUS. 


PHYSIOLOGY:   PRACTICUM   VIII:    PLATE  XVIII. 


THE  RRAIN  OF  THE  SHEEP,  THE  CEREBRUM  SLICED  TO  NEAR  THE  LEVEL 
OF  THE  CALLOSUM  ;   X    1.5. 


-  olfactory    bulb  inclosing  rhinoccele 


'--genu  (of  callosum) 
--cortex  (cinerea) 
medulla  (alba) 

—  Sylvian  fissure 
— callosum 


-  F^  —  spleniuni  I  of  callosum) 


C — r^^:s:^f'^^'~f vermis  imcsal  lobe) 

lateral  lobe 


poitoblongata 
myel  (spinal  cord) 


The  following  points  are  illustrated  : 

A.  The  general  proportions  of  the  two  great  masses,  CEREBRUM  and  CEREBEL- 
LUM. 

B.  The  constitution  of  the  cerebellum  bv  a  mesal  lobe  (VERMIS)  and  a  pair  of  LAT- 
ERAL LOBES. 

C.  The  junction  of  the  two  halves  of  the  cerebrum  by  a  thick  sheet  of  fibers,  the 
CALLOSUM  ;  its  rounded  cephalic  and  caudal  margins  are  the  GENU  and  SPLENIUM, 
respectively  ;  PI.  XXIII. 

D.  The  relative  positions  of  the  two  kinds  of  substances  in  the  larger  part  of  the 
cerebrum  ;  the  ALBA  (white  substance)  is  central  ;  the  CINEREA  (gray  substance),  is  per- 
ipheral, constituting  the  CORTEX. 

E.  The  relation  of  the  corte.N;  to  the  FISSURES. 

F.  The  passage  of  the  ARACHNOID  membrane  across  the  mouths  of  the  fis.sures,  as 
at  I  and  4,  while  the  PIA  dips  to  the  bottom  as  a  fold. 

G.  The  existence  of  a  cavity  (RHINOCCELE  or  olfactorv  ventricle)  in  the  OLFAC- 
TORY BULB  ;  see  PI.  XXIV  and  p.  69,  Fig.  3. 

Defects.— Th.^  cerebellar  divisions  (FOLIUMS)  are  not  shown  in  detail.  In  the  dark 
interval  (6)  between  the  cerebellum  and  cerebrum  should  appear  the  cut  ends  of  vessels 
one  of  which  is  shown  in  PI.  XXIV.  There  is  no  indication  of  the  thin  layer  of  cinerea  on 
the  dorsum  of  the  callosum  ;  PI.  XXV. 


PHYSIOLOGY   :    PRACTICUM    VIII    :   PLATE   XIX. 


VENTRAL  ASPECT  OF  THE  SHEEP'S  BRAIN  WITH  THE  EYES  AT- 
TACHED; X  1.3. 

From  the  specimens  commonly  examined  the  brain  here  represented  differs  as  follows  : 
a.  The  EYES  have  been  retained  with  OPTIC  NERVES,  b.  The  HYPOPHYSIS  is 
retained.  c.  Besides  the  TRIGEMINUS  NERVES  (marked  5),  on  the  actnal  brains 
there  are  more  or  less  distinct  signs  of  the  roots  of  the  other  cranial  nerves. 

The  numbers  indicate  parts  as  follows  :  i,  a  small  portion  of  the  PALLIUM  or  fissured 
region  of  the  CERREBUM,  projecting  mesad  of  the  OLFACTORY  BULB.  2,  the  OL- 
FACTORY CRUS,  connecting  the  OLFACTORY  TRACT  with  the  BULB.  3,  a  slightly 
depressed  area  just  cephalad  of  the  OPTIC  TRACT.  4,  a  part  which  distinctly  projects 
over  the  tract.  5,  The  root  of  the  TRIGEMINUS,  the  great  sensory  nerve  of  the  face.  6, 
a  slight  ridge,  not  always  distinct,  crossing  the  CRUS.  7,  the  TRAPEZIUM,  concealed  in 
the  human  brain,  by  the  caudal  margin  of  the  broad  PONS.  8,  the  PYRAMID,  less  dis- 
tinct than  in  man  and  not  exhibiting  a  DECUSSATION. 

Some  details  are  more  fully  shown  in  PI.  XX. 


PHYSIOLOGY:    PRACTICUM    VIK:   PLATE   XX. 

BASE  OF  SHEEP'S  BRAIN  AFTER  THE  REMOVAL  OF    THE    HYPOPHYSIS 
AND  PARTS  OF  THE  CEREBRUM  AND  CEREBELLUM  ;  enlarged. 


olfactory  bulb 


INSULA 
olfactory  fissure 


PREGENICULUM 

POSTGENICULUM 

CRUS 


CEREBELLUM 


The  cephalic  and  caudal  regions  are  nearly  the  same  as  in  PI.  XIX,  but  the  following 
differences  should  be  noted  :  a.  The  absence  of  the  frontal  "parts  of  the  cerebrum  be- 
tween and  laterad  of  the  OLFACTORY  BULBS,  b.  The  indication  of  the  MESAL  (i) 
and  LATERAL  (2)  ROOTS  of  the  bulb.  c.  Between  the  two  the  irregular  triangular  area, 
PRECRIBRUM  ("anterior  perforated  space")  presenting  orifices  for  the  transmission  of 
vessels,  d.  The  removal  of  the  HYPOPHYSIS  ;  this  exposes  a  slight  elevation,  TUBER, 
and  an  orifice,  lura,  leading  into  the  diacoele.  e.  The  CRURA  and  OPTIC  TRACTS 
are  more  fully  seen.  f.  The  PONS  presents  more  distinctly  the  mesal  emargination  of 
its  caudal  margin. 

I,  Mesal  root  of  olfactory  bulb.  2,  lateral  root.  3,  cut  surface  of  olfactory  tract  and 
pallium.  4,  depression  caused  by  the  extraction  of  the  right  oculo-motor  nerve.  5,  Cau- 
dal emargination  of  the  pons.  6,  Ventral  mesal  sulcus  of  the  oblongata.  The  unnamed 
shaded  line  across  the  cms  just  cephalad  of  the  oculo-motor  nerve  was  intended  to  repre- 
sent the  cimbia. 


PHYSIOLOGY  :    PRACTICUM    VIII  ;    PLATE  XXI. 

LFFT  SIDE   OF   THE   SHEEP'S   BRAIN   AFTER   THE   REMOVAL   OF   MOST   OF 
THE   CEREBRUM  AND  CEREBELLUM  ;  X   i- 


Cfinarium 


o^-^ 


^■cN^         thalamuij       i        _,^  , 


i? 


4'       ^  pons  postobloiigJta 


The  CEREBELLUM  is  left  of  its  natural  height,  but  the  cephalic  and  caudal  convexi- 
ties are  sliced  away  so  as  to  expose  the  parts  which  are  overhung  b}'  them.  In  a  compan- 
ion preparation  the  dorsal  portion  of  the  cerebellum  has  also  been  removed,  with  the 
cephalic  and  caudal  convexities,  but  the  lateral  "overhangs"  are  retained. 

The  CEREBRUM  has  been  cut  down  to  the  level  of  the  THALAMI  ;  the  caudal  por- 
tion cut  away  along  the  oblique  line  of  its  projection  over  the  part  marked  5  ;  the  lateral 
portion  so  as  to  expose  the  part  marked  3  ;  also  the  cephalic  projection  which,  as  seen  in 
Plates  XIX  and  XXV,  overhangs  the  OLFACTORY  BULBS. 

The  short  lines  on  the  surface  of  the  olfactory  bulb  represent  the  OLFACTORY 
NERVES.   The  cut  end  of  the  left  OPTIC  NERVE  is  dotted  to  indicate  its  fibrous  structure. 

I,  OLFACTORY  CRUS  ;  compare  with  PI.  XX.  2,  a  part  of  the  PALLIUM  which  has 
not  been  cut.  3,  OLFACTORY  TRACT.  4,  (indistinct),  CHIASMA.  5,  PREGENICU- 
LUM  (external  or  anterior  geniculate  body),  distinct  in  man  but  here  little  more  than  a 
lateral  portion  of  the  thalamus.  6,  TUBER  (c;«frf?;w/),  the  slight  convexity  to  which 
the  HYPOPHYSIS  is  attached  ;  in  PI.  XX  it  is  the  area  just  caudad  of  the  chiasma.  7, 
the  MEDIPEDUXCLE,  continuing  the  PONS  to  the  lateral  mass  of  the  cerebellum.  6, 
the  TRAPEZIUM  ;  compare  with  PI.  XX. 

Excepting  the  unshaded  areas,  representing  cut  surfaces,  all  the  parts  seen  in  this  fig- 
ure were  covered  by  PIA. 

At  the  dorsal  end  of  the  cerebellum  are  seen  a  few  FOLIA,  its  leaflet-like  divisions  ; 
these  are  not  shown  in  anj'  other  plate. 

Besides  facilitating  the  recognition  of  certain  important  parts  this  figure  well  illus- 
trates the  srgmetital  constitution  of  the  brain,  which  is  obscured  in  the  entire  organ  by  the 
preponderance  of  the  cerebrum  and  cerebellum.  There  is  a  series  of  more  or  less  distinct 
masses  demarcated  by  constrictions  of  greater  or  less  depth.  Admitting  that  there  is  still 
some  doubt  as  to  number  and  limits  of  the  segments  the  following  assignments  may  be  ac- 
cepted provisionally  : 

Olfactory  bulbs  and  crura,    \  RHINENCEPHAL. 

Cerebrum    ]   PROSENCEPHAL  (fore  brain). 

Thalami,   conarium,   hypophysis,   \  niENCEPHAL  (inter-brain), 
chiasma,    and   geniculums,    J  ■ 

Geminums  and  crura    |-  MESENCEPHAL  (mid-brain). 

Cerebellum,  pons  and  preoblongata,    ]-  EPENCEPHAL  (hind-brain). 

Postoblongata    1    METENCEPHAL  (after-brain). 


PHYSIOLOGY:  PRACTICUM   VIII  :    PLATE   XXII. 

DORSUM   OF   SHEEP'S   BRAIN   AFTER   THE   REMOVAL   OF   PARTS   OF  THE 
CEREBRUM   AND   CEREBELLUM. 


Litercerebral  fissun 

SJ'lv 


olfactory  biilbl 

,       /    I  7  j  RHINENCEPHAL 

olfactory  cms  I 

1  1 

caput  of  caudatum   j 

Iprosence- 

msula  I  PHAL 

V    '\    \  ^        -  Cauda  of  caudatum  J 

;^Y!\T" — 7 habeua  1 

rTTW medicommissure 

,  n'^^n/vI thalamu.s  .^DIENCEPHAL 

V    '^LD^ preg-emculum 

*^     '  postgeniculuni 

ff^^  couarium  ' 

pregemiuum    1 

'-MESENCEPHAI, 
postgemiuura  ) 

,^£^ pons  I 

X'-l  flocculus  l-EPENCEPHAL 

—  cerebelluui 


postoblongata    j- METENCEPHAL 


Compare  with  PI.  XVIII.  From  the  cerebellum  have  been  cut  the  dorsal  part 
and  also  the  caudal.  On  the  cut  dorsal  surface  are  seen  the  central  alba  and  the  periph- 
eral cinerea,  but  the  outline  of  the  latter  is  diagrammatic  onl)'.  At  the  sides  are  the  tiers 
of  foliums  constituting  theflocculus. 

From  the  cephalic  end  of  the  cerebrum  have  been  cut  the  parts  projecting  over  the 
olfactory  crura,  but  part  of  the  cephalic  slope  marked  b  in  PI.  XVIII  is  here  marked  1. 
With  the  dorsal  portion  were  removed  the  entire  callosum  and  the  fornix  excepting  the 
cephalic  vertical  part.  This  and  the  mesal  walls  of  the  paraccEle  are  really  cut  at  a  lower 
level  than  the  larger  cut  surface  on  the  left.  On  the  rigiit  the  insula  has  been  exposed  by 
pushing  up  and  breaking  off  the  overhanging  parts.  The  ectal  surfaces,  covered  by  pia, 
are  indicated  by  irregular  lines  representing  the  blood-vessels. 

The  ental  surfaces,  covered  by  endyma,  are  those  of  the  caudatums  in  the  paracoeles, 
the  habenas,  medicommissureand  conarial  pouch  ;  and  the  floor  of  the  aula  and  purtas. 

The  irregular  line  laterad  of  the  habena  and  extending  around  the  endj'mal  area  on 
the  conarium  represents  a  ripa  (shore-line).  It  consists  ol  the  cut  or  torn  edges  of  the  pia 
from  the  dorsum  of  the  thalamus  and  of  the  endyma  from  the  habena  which  united  to  form 
a  membranous  roof  of  the  diacoele,  the  DIATELA,  which  has  been  removed. 

Similarly  the  pial,  dorsal  surface  of  the  thalamus  is  demarcated  from  the  endymal  sur- 
face of  the  caudatum  by  a  ripa  which  meets  the  other  at  the  porta. 

The  CONARIUM,  although  a  constituent  of  the  DIENCKPHAL,  is  tilted  caudad  so  as 
to  rest  upon  the  PREGEMINUM,  and  the  niesal  part  of  its  exposed  surface  is  likewise 
covered  by  end}'ma. 

I,  cephalic  slope.  2,  mesal  wall  of  PARACCELE  ;  at  a  higher  level  this  would  be  one 
of  the  HEMISEPTUMS.  3,  horizontal  cut  surface  of  cerebrum.  4,  the  mesal,  vertical 
portion  of  the  paracoele.  5,  indicates  the  location  of  the  ripa  between  the  thalamus  and 
caudatum,  but  it  is  overhung  by  the  latter  so  as  not  to  appear  in  this  view.  6,  extension 
of  the  diacoele  upon  the  conarium.     7,  mesal  furrow  of  the  pregemiuum. 


PHYSIOLOGY:    PRACTICUM    IX:   PLATE  XXIII. 
MESAL   ASPECT   OF   RIGHT   HALF   OF  SHEEP'S  BRAIN  ;    X  2. 


f      — ■ spkiii  il  iissure 

^      f .Iwttli 

'"■^  luUiji 


,     ,  ,         C^  ^.^  °-'^  "J^ 


This  figure  is  semi-schematic,  certain  details  being  omitted  for  the  sake  of  clearness, 
e.  g.,  the  divisonsof  the  CEREBELLUM,  the  VESSELS,  and  the  MEMBRANES,  ARACH- 
NOID and  PIA.  The  pia,  however,  is  represented  by  the  line  between  the  ROSTRUM  and 
the  CRISTA. 


The  tuber  is  the  Tuber  cinereum,  called  torus  in  the  former  edition. 


The  objects  of  the  figure  are  :  To  show  most  of  the  MESAL  PARTS;  to  illustrate 
ENDYMAL  CONTINUITY  and  its  concomitant,  CCELIAN  CIRCUMSCRIPTION  ;  to  in- 
dicate the  PLANES  OF  TRANSECTION  which  are  most  instructive,  A—G.  Compare 
Plates  XX,  XXII,  XXIV  XXV.    For  fuller  description  see  Practicum  IX. 


PHYSIOLOGY:    PRACTICUM    X:   PLATE   XXIV. 
SHEEP'S  BRAIN,  THE   PARACCELES  (lateral  ventricles)  EXPOSED  ;  X  2. 


This  figure  represents  a  stage  of  dissection  intermediate  between  Plates  XVIII  and  XXII. 
By  the  removal  of  successive  slices  the  PARACCELES  have  been  opened  ;  the  left  has  then 
been  more  completely  exposed  by  oblique  sections,  and  the  PARAPLEXUS  trimmed  off 
so  as  to  expose  the  wide  FIMBRIA  and  the  furrow  between  it  and  the  HIPPOCAMP.  The 
plane  of  section  did  not  coincide  exactly  with  the  CALLOSUM  ;  the  caudal  three-fifths  of 
this  is  represented  by  the  transverse  lines  ;  also  the  cephalic  end,  the  GENU  ;  but  an  in- 
termediate portion  is  wholly  removed,  exposing  the  narrow  PSEUDOCCELE  ("fifth  ven- 
tricle") and  its  thin  lateral  walls,  HEMISEPTUMS.  The  HEMISEPTUM  is  here  shown 
to  be  only  a  porion  of  the  general  mesal  wall  of  the  paracoele.  The  Pseudoccele  (PI. 
25)  has  no  connection  with  the  true  cavities  of  the  brain.  The  only  communications  of 
the  paracoeles  are  through  the  PORTAS  with  the  mesal  AULA  (PI.  XXII). 

The  two  FIMBRIAS  and  HIPPOCAMPS  connected  by  a  mesal  part  (PI.  XXV)  consti- 
tute the  FORNIX. 

The  HIPPOCAMP  is  sometimes  called  hippocainpus  major. 

I,  INTERCEREBRAL  FISSURE.  2,  CALLOSAL  FISSURE.  3,  VESSEL.  4,  inter- 
rupted lines  indicating  the  continuation  of  the  paracoele  into  the  RHINOCCELE.  5, 
PRECORNU.  6,  CAPUT  of  the  CAUDATUM.  7,  SYLVIAN  FISSURE  crossed  by 
ARACHNOID.  8,  VESSEL  at  bottom  of  fissure.  9,  CAUDA  of  CAUDATUM.  10,  part 
of  caudal  wall  of  paracoele. 


PHYSIOLOGY  :   PRACTCUM  IX  :   PLATE  XXV. 
A.     TRANSECTION  OF  SHEEP'S  BRAIN  ;    ■    1.5. 


irachnoid 
ntercerebral   fis 


HABENA 

MEDICOMMISSURE 

diaccele 


optic   tract 
olfactory  tract 


The  plane  of  section  approximales  E  in  PI,  XXIII.  The  HYPOPHYSIS  has  been  re- 
moved and  the  DIACCELE  is  open  ventrad  at  the  LURA  (PI.  XX).  The  OPTIC  TRACT  is 
cut  obliquely  ;  its  fibrous  structure  is  roughly  indicated  bv  lines.  The  masses  connected 
by  the  MEDICOMMISSURE  are  the  THALAMI.  The  CALLOSUM  is  indicated  by  lines. 
The  INTERCEREBRAL  FISSURE  is  bridged  by  the  ARACHNOID  ;  in  man  the  'falx  de- 
scends into  the  fissure  for  a  greater  or  less  distance  carrying  the  arachnoid  before  it.  The 
fissure  here  named  rhinal  is  named  olfaciory  in  PL  XIX. 


B.  ENLARGEMENT  OF  THE  CENTRAL  REGION  OF  A, 


intercerebra]  f. 
pia 

— cortex 

callosal  fissure 
callosal  cinerea 


ENDYMA 
--   paracoele 
J_    PSEUDOCCELE 
»__   HEMISEPTUM 

foruicom  missure 

VELUM 
■=-    velar  vein 
- —    RIPA 

DIATELA 
-^^   DIAPLEXUS 
diaccele 

raediconimissure 

This  wasdesigned  to  eshibit  more  clearly  the  relations  of  the  CAVITIES  to  the  MEM- 
BRANES  and  PLEXUSES,  but  some  points  are  obscured  by  the  shading. 

The  mesal  DIACCELE  and  the  lateral  PARACCELES  are  lined  by  smooth  ENDYMA, 
represented  bj' a  heavy  line.  In  the  diacoele  the  endyma  may  be  traced  dorsad  upon  the 
mesal  surface  of  the  THALAMUS  and  over  the  dorso-mesal  ridge  representing  the  HAB- 
ENA, as  far  as  the  point  called  RIPA,  (see  PI.  XXII,  left  side.)  Here  it  is  reflected  mesad 
upon  the  ventral  surface  of  the  VELUM 

The  velum  consists  of  the  PIA  covering  the  ventral  surface  of  the  FORNIX  and  the 
dorsal  surface  of  the  thalami.  together  with  CONNECTIVE  TISSUE  and  VESSELS  (of 
■which  only  one  is  shown).  Near  the  meson  there  hangs  into  the  diacoele  at  each  side  a 
plexus  (DIAPLEXUS)  covered  by  the  endyma. 

At  the  interval  (RIMA)  between  the  margin  of  the  fornix  and  the  caudatum  (i)  the 
velum  extends  into  the  paraccele  as  the  PARAPLEXUS,  covered,  however,  by  the  endyma 
which  is  reflected  off  at  3  and  the  point  opposite. 

A  thin  layer  of  the  cortex  extends  across  the  callosuni. 


COLUMBIA  UNIVERSITY  LIBRARIES 

This  book  is  due  on  the  date  indicated  below,  or  at  the 
expiration  of  a  definite  period  after  the  date  of  borrowing, 
as  provided  by  the  rules  of  the  Library  or  by  special  ar- 
rangement with  the  Librarian  in  charge. 

DATE  BORROWED 

DATE  DUE 

DATE  BORROWED 

DATE  DUE 

& 

PRi  2  ^y*^ 

c.en,.o,„,oo 

OPS  76 

Mlder 


F64 

1695 


